In the repair space, both Apple official and third-party especially, these units are known for their very poor reliability. They have a number of hardware faults on them. The first major one is the infamous butterfly keyboard, which is known to basically spontaneously develop failures from usage and can present itself in the form of hitting a key and then multiple letters enter at once, or hitting a key and nothing happens, or the keys themselves getting physically crunchy or jammed, and in some cases even the entire keyboard flat out dying, and there isnt much peventative measures to take other than not using keyboard. If that wasn't bad enough, these things also have a fun tendency of developing a lot of logic board related issues, particularly with the CPU's dying/failing in fun ways. Usually symptoms of this would be things like memory failures, graphical artifacts typically because of the memory failures, kernel panics and random crashes especially under load, the storage drive completely disappearing from the system and now showing up as a connected piece of hardware and the machine being unable to boot, add some cases the machine can also flat out die completely and basically show no signs of life other than a trackpad that clicks whenever the unit is charged. There's no real remedy or solution for this other than replacing the logic board, but the replacement boards will also fail in the same way eventually and at this point you're either paying crazy money for a refurbished board from Apple or marginally more reasonable but still expensive used boards but they come from God knows where with what kind of history so it's basically a gamble anyways. Because these machine machines are worth so little and the cost of repairs is still a lot for many things, even something as straightforward as battery service from Apple basically puts these machines in the red in terms of overall costs. Cheaper through third-party but then you run into the same sort of gamble style problems where the parts themselves in that field tend to be pure crap more often than not, or in rarer cases like iFixit, expensive but mediocre (and at least wont kill the unit unlike ebay and amazon and such). At that point if you're hit with basically any hardware problem on these machines, it pretty much immediately becomes a situation where the cost of repair plus what you initially paid for the unit starts to just get dangerously close to the cost of a base model M1 MacBook Air, which will not only substantially outperform it but have a ton of other benefits in the form of better battery life and better thermals and also running silent and being a lot more reliable and actually having support from Apple for the next half a decade if not more.
Assuming all of the hardware is perfect and assuming none of these age related issues this machine that you might purchase, you're not out of the woods yet. The operating system side of things is also gonna be a problem in most of these cases and will require you to put in a whole bunch of extra work. Both the 2015 and the 2016 model at this point our end of life and no longer receive any sort of maintained macOS version, since both of those are stuck on BigSur and monterey respectively, while the 2017 model supports Ventura, which is going end of life later this year around November/December so it's not particularly far behind. Luckily unlike the hardware issues above, these ones you can mitigate with a bit of effort on your part. You can basically trick these machines into taking a newer version of macOS than what the unit supports using OpenCore Legacy Pactcher, which will basically allow you to install Sonoma and Sequoia unofficially on the units with a little bit of work, and both of these gill give you over 1.5years and 2.5years of support and bugsixes and security mitigations respectiely. Alternatrively, you can patch Windows11 to install on these units (with some work) and thatll be suported for a while still, and there is always good ol' Linux, which will be supported until the end of time and nothing will run as smoothly as that, since Linux is designed for old systems from the start and will even run of rocks on the side of the road if it needs to. Any OS older than whats mentioned here at this point you shouldnt really be using due to its entirely unmaintained nature, which makes them a security problem, and that gets even worse the further behind the curve you fall. Even if we put our heads in the sand and pretend that security is not important and ignore all the real world problems that exist, as obfuscated and abstract as they may be, simply running these old operating systems will eventually catch up to you anyways in the form of application support not existing, old apps eventually breaking, and in general just not supporting modern technologies and features which can also catch up to you in various forms. Basically just shooting yourself in the foot intentionally running something old and just unnecessarily adding risk to your life, regardless of what perspective you use. With OCLP Sonoma/Sequioa, or Win11, or Linux, you can absolutely stretched a little bit of extra life out of these machine, and many of these will actually run perfectly fine with a little bit of work, but if you haven't done stuff like that or aren't familiar with it, you're gonna have to get involved and potentially start learning new stuff and be comfortable with sometimes reading technical stuff if things go wrong. Basically the nature of the beast whenever you try to maintain 10+ year-old computers.
If you want to get one of these 12 inch units just for collecting purposes, totally fair, and you can put in a bit of time to get a not-unmaintained operating system onto it to mitigate a lot of the problems and then just keep up on the updates with it, but if you're looking to actually daily drive something, or even as some secondary unit, you should just entirely ignore the 12" macbook lineup, and quite frankly the rest of the Intel Mac lineup as a whole since a good chunk of them have overlapping issues with reliability and support and just pedestrian performance by 2025+ standards, especially in a post-Apple SIlicon world. If youre going to spend a couple hundred on a unit, as a main or secondary, it at least should get your moneys worth and not be a burden/liability. Something like a used M1 MacBook Air is very cheap for 8Gb variants these days,w which can be found for as low as 400USD used, and the more ideal 16GB versions are closer to 500-600usd and a better purchse anyways. Alternatively an iPad with the keyboard case of sorts will go a long way sepecially since iPadOS is fairly mature and a lot of peoples apps are all just web-apps or running in a web-wrapper anyways (stripped down browser engine for rendering stuff), or even some of those smaller form factor to retired enterprise-grade fleet Windows laptops (lineups like: Dell Latitide, HP Elitebook, HP Probook, Asus ExprttBool, Lenono Thinkpad), which can be made for wither WIn11 or Linux, and can be found with crazy good spec like 16GB/512GB and 8th gen or higher properly cooled faster Intel CPU for under 250USD, and also hae room to upgrade storage or memory and be way cheaper to fix if it breaks. Any of these are going to be a much better solution for a small portable system that's gonna require basically no additional work on your end to keep it maintained and secure and supported, it will not have any of the major reliability issues a lot of these 12-inch units run into, and will often outperformed them pretty much across the board for relevant things like battery life and thermals and actual performance and stuff like that.
I use to daily drive one for many years around late 2010's, and I have a mint unused 2015 in my closet atm with new top case and sub-50 cycle battery purely for collecting. I loved it to bits as a tiny women with tiny hands and weak shoulder muscles with a more loaded purse, but id never recommend getting one now beyond a super cheap hobbyist tinker machine that you know can become a totalled sunk cost at any moment due to hardware, or just for collecting in a closet because youre obsessed with Mac. I've probably spoken to thousands of owners of these 12" units over my tenure of receicing appointments from Apples system, and many are crazy about these due to size, but ive had this exact convo with so so so many of them and seen people spend crazy money upkeeping one that it just turns into a money sinkhole and they couldve bought multiple used M1 airs by then. If they made an apple silicon 12" I wouldnt even hesitate buying one, but the existing ones have too many downsides from a number of perspectives to be worth anything for 99% of users
