I'll preface it with the fact that when they work, they work very well.
But, about once a year or so, I've had access points and the cloud key just randomly fall off and then it's a pain in the ass to provision...as in, it won't, or it's not just a simple re-provision and it's back working. Or, just other minor things. Hell, when I went to log in to take the picture of my setup for this thread, I logged into the cloud key and then went to log into the unifi dashboard and it didn't work. Stopping and starting unifi in the cloud key didn't work, but rebooting the cloud key did. Just little things like this, but it seems to happen a lot.
I'm fortunate enough to live in a very large, very nice house where I need multiple access points to cover the whole area. I added my last In-Wall AC Pro about a year ago to my living room where I had okay 2.4G coverage but poor 5G. I just recently received a message that the In-Wall AC Pros are EOL. Man, I get it...the next generation are on their way in. But, it seems like I just got these.
I've had no problem with my POE switch, I even bought it used on ebay. It was a little loud, so I swapped out the fans for Noctuas. If I had a complaint, it would be that the interface is probably a little more focused on being pretty than ease of use for setting up VLANs, etc. Just my opinion though and once I learned it, I've been okay with it. I'm not really a fan of how they look. I mounted it to the back side of my rack so it wouldn't be seen LOL. That's just personal opinion too.
To Ubiquiti's defense, I did have one access point just fall off and I couldn't re-provision. I messed with it for a couple hours...reset, factory reset, etc and it still didn't work. Ubiquiti sent me a brand new one...I had it in two days and used the box to sent back the old one. I always say that it's not if a product or service messes up, but how a company handles it and I couldn't ask any more from Ubiquiti or their support.