It's funny, Ubiquiti keeps getting talked up on HN, but every time I try to shop for their equipment out of curiosity, it's basically panned everywhere else. Don't know what to make of it.
But I said had, because in 2020 the company seems to have transformed into a money-grabbing shitshow. Cloud for everything, deprecating fine hardware and fine software in favor of unneeded cloud stuff. Crappy firmwares with no easy way to rollback. CEO is supposedly running the company in the ground with outsourcing, constant crunch etc. There are some disgruntled ex ubiquity employees here and on reddit, if even half is true of what they say the company really needs to turn around soon, it is probably already to late.
Same mass-market Qualcomm SOCs as the other mass-market vendors, just better packaged and marketed.
Smallnetbuilder consistently found them middling in performance.
I have one of the flying saucer shaped APs, but it's super old and only does B/G. It was under a hundred bucks and unlike my old APs it doesn't get angry at certain devices and deauth them randomly from the network. Or other APs I've used that start disconnecting users once you have more than 15 devices connected at once. The configuration software is a bloated Java daemon that I have to manually start then connect to with a client. It's not all that user friendly, but I've been around networks enough to get it working.
So it's basically the cheapest AP that isn't regularly malfunctioning consumer garbage.
Their security gateways are universally hated on, and for good reason - one major one is that enabling DPI causes a ridiculous drop in throughput rate, even on the newer machines (which also have faulty firmware). Stay away from them.
I eventually got a TP-Link WiFi 6 AX3000, and it's been super solid, significantly faster, and required almost zero manual setup. The Unifi itself required a PoE adapter and a router, and of course needs the controller application to do anything.
(The controller app with its easily-corrupted and hard-to-upgrade MongoDB database is perhaps the worst part of it. My two devices occasionally required re-"adopting" for no discernible reason. I was unable to upgrade the controller at one point because apparently (?) they stopped bundling MongoDB, and the controller refused to use the version I installed manually. Of course, this breakage happened after the software updated, so the only way to fix it was by restoring the old version and database files from backups.)
Maybe Ubiquiti products make more sense when you need dozens of access points across a big building, but definitely not in a small city apartment.
The Unifi Security Gateway is a router.
My wish is for a prosumer wireless router that's rock stable. I've burned through numerous routers that all have had weird issues. The closest I've gotten was my Microtik AC Lite, which I loved, but it doesn't have an external antenna, so its range was questionable.
AFAIK, only the 5-piece package ships without injector, the individual ones do have it.
I've purchased only nano-HDs and AC-lites, and they all came with one in the box. What didn't have any is Cloudkey 2 Plus. I had to get a third-party injector for that one (or Quickcharge USB charger with USB-C cable - I went with injector).
I have an Edgemax ER-Lite router and a UAC-AP-Pro access point, and a security camera for testing.
If you can, it's best to stick with one lineup of products. Unifi is one line, edgemax is another, amplifi is another, and so on - having one management plane is optimal. I have thought about getting a Unifi router so everything is done through one control center, but I don't need to.
tl;dr - I think they are great for the money. You can do advanced stuff with the routers as well, like VPN gateways and BGP if needed, but not always easily in the GUI.
Meraki would be nice except Cisco owns it now and they are experts at milking you with annual fees.
Why just replace them with second hand units?
Apple may no longer sell them, but they are still widely available.
I've had UniFi equipment for a while now and am generally happy with it, though I'm not doing anything terribly crazy. Well, maybe crazy for a home user, but not nearly as crazy as some of the /r/homelab folks get.
I've got multiple VLANs, firewall rules controlling traffic, multiple WiFi networks. I'm using 2 switches (8 port 150W PoE, 24 port non-PoE), a USG, and an AP AC Pro. It all works fine.
My only complaint is that the new version of the controller software rearranged all of the settings and I haven't figured out where everything lives.
There's also a search in there which has proved helpful.