I have a UniFi AP and a 24-port 10G switch from Ubiquiti. As far as 6. goes, you are sadly correct. It’s all Linux underneath so there are plenty of changes you can make in the CLI, but the middleware will happily stomp all over it at the next upgrade or reboot.
For no cloud, it’s quite easy to avoid. The middleware can be spun up in a container or installed on any Linux VM and have no access to Ubiquiti’s servers at all and it’ll work fine (you’ll have to upload updates yourself). However, the product will be full of little nagging notices coaxing you into going to the cloud, or as in my case, getting mad you aren’t using a UDM for your router/firewall and turn off a bunch of the L3 features. The software is meme-level in how many bad patterns and form-over-function decisions are in it. Cloud or no, it’s frankly kinda crap.
The APs are solid, but I’ll likely not buy another switch from them if I can help it. Depending on your needs, there is plenty of used enterprise gear to be had for quite cheap on eBay. But, I’m in the market for a fat 48-port switch with a huge PoE budget and they have one that’s all 2.5G. I don’t know that anyone else makes one, and if they do, it’s three times the price, or I have to call some sales person to talk about it, or the actual existence of the product is impossible to surmise through thick marketing wank datasheets.