Just to bump & continue this topic, those open-bottom iPhone 12 silicone cases were pretty good. I ordered two, but now more than 4 months later I'm still on the first one, without much wear, apart from the subtile grey Apple logo on the back that will wear off the silicon. No big deal: once gone it's better! But it feels pretty much like the original 12 silicone case, except for the open bottom.
I see they're not available anymore through my link above, as usual with most of those products on AliExpress after a few months (although I still think you'll find them on there, if you scroll long enough!). Probably due to the counterfeit packaging, which was indeed an EXACT copy of the apple case package, including Apples address etc. Apart from that that's clearly illegal, I really wonder why they pretent to be apple on the packages, because this has totally no value to me.
But on the topic of open vs closed bottom cases, I'm REALLY wondering why Apple has moved to closed bottom! All the modern iOS gestures feel *much* better and easier to do without a lip on the bottom side. Especially, the multitasking gestures for all-screen iPhones.
It's too bad those open-bottom iPhone 12 cases are getting more rare now, as they all want to copy Apples closed bottom. I'm also really amazed that there aren't much complaints on the MacRumors forums about this move by Apple!