I have 4 Airport Extreme AC (well, one is a Time Capsule, but same thing) all connected via ethernet backhaul for full house & yard coverage. Apple released a firmware update a few months ago. Until they stop completely, I will continue using them.
Used to have 3 Airport Extremes configured with a single SSID for both 2.4GHz and 5GHz networks. If a device had a poor 5GHz signal, it would automagically switch over to the 2.4GHz network. Everything worked like a charm. Then I saw all these sexy adds for new mesh wifi systems with per-device analysis, small sized units to fit almost anywhere (and thus didn't need to be near my ethernet jacks) and all sorts of other interesting features. They won me over and I bought and installed the Google Wifi mesh system (the short, cylindrical ones; since renamed Google Hub Wifi or something like that). All my Apple devices and my Ring doorbell hated it. Worked fine for everything else, but none of my Apple devices would hold the wifi signal for more than a few minutes without dropping then restoring. It was incredibly frustrating. The Ring was similarly unstable and even ended up using an Airport to give it it's own separate wifi work. Whole thing was a mess and only ended up making things far more complicated than it needed to be. Went from having one unified wifi network with a single SSID to two different wifi systems with a total of three separate SSIDs (in attempt to stabilize the various devices from dropping signals by locking them to one of three networks -- two 2.4GHz and one 5GHz). In certain parts of the house, we'd have to manually change from one network SSID to another when the 5GHz would drop low enough to not work well, but not low enough that the device would automatically switch to the differently named 2.4GHz network. And, at least at the time, putting the Google wifi in bridge mode killed almost all of the fancy per-device features, so I was forced to have a double NAT behind my FiOS router, which I didn't want (caused problems for a few devices connected via MoCA).
Ripped out the Google wifi and replaced it with a top of the line Netgear Blackhawk something (can't recall which model) that I paid a pretty penny for. Seemed to work ok... good speeds, almost as good range (dropped off before the end of the yard but that was one unit vs. previous mesh of three). Meshing it with a signal repeater to get better coverage at one far end of the house cut speeds in half. And, somehow, it blew itself out after two weeks -- device died and wouldn't power up. Plus, to get enough coverage without meshing, it had to sit squarely in the center of the house and be close enough to either the FiOS router or an ethernet port, limiting my placement options for, shall we say, spousal aesthetic approval. Had to return it.
Put the Airports back in, and have been trouble free ever since. Even bought another one off eBay to add another node. Happily ran bridged to ethernet over MoCA. The Airports can all go into bridge mode to prevent issues with double NAT, all work fine with an ethernet backhaul (instead of mesh-over-wifi), and all my devices -- Mac, PC, iOS, Nest, etc. -- work perfectly with them without needing to resort to separate SSIDs to appease different devices.
I've since moved and replaced the Ring, but still use the 4 Airport Extreme AC units in bridge mode connected via gigabit ethernet instead of mesh-over-wifi, and couldn't be happier. Still see discussions about certain cool-sounding features that newer systems have, but until I'm convinced that they'll "just work" like the Airports, I'm sticking with what I have.
