Ubiquity is trash with fickle support based on the whims of what sells wide adoption. TP Link IMO is a decent value for the money if you want easy “prosumer” level networking gear. I have I have 3 TP Link APs as well as a 16 port 10g core switch and its great for my needs.
Mikrotik offers more features per $$ but its not as easy to use.
Used UPS’s show up from time to time. I recently found a craigslist posting with 6 all of which were in decent shape needing some cleaning, and new batteries.
Batteries are the rub since they only last about 5 years so most used ones need new batteries. Good news is its not that hard to replace them as long as you take your time and pay attention.