Zero Handoff Roaming only really works in very specific environments. The way it works is by having all of the APs on the same channel and spoofing data to appear as if it is coming from the previous AP. The APs figure this all out by communicating with each other over an encrypted connection on the LAN. Anyway, basically it only works when your APs are the *perfect* distance apart to avoid serious channel congestion, interference and poor performance. Honestly it is a PITA to get right and I would avoid it like the plague.

With normal setups it is the client itself which is the device that decides to move from one AP to another. A decent client will typically switch networks in around 500ms and this shouldn't really affect anything bar maybe a blip in SIP VoIP.

It is true that historically Ubiquiti have released some products before they are ready. Don't touch the USG. The v1 UAP-AC was also a fairly terrible product (the current UAP-AC v2 is not bad). The UVP phones are a little raw at the moment software-wise.

On the flip side the UAP-PRO is a great piece of kit, and the plain vanilla UAP is amazing value for money in rural situations where 2.4GHz is not congested. Don't bother with the UAP-LR as it really doesn't offer anything over the UAP. Personally, I find the software controller to be reliable. It is not the best designed thing, but it does work well.

Yes, the UAP products I mentioned are EOL. The new generation of UAPs are all AC. They all have their merits - the UAP-AC-LITE is really quite cheap for what it is and a good unit for low bandwidth use with its 2x2:2 setup on both channels. The UAP-AC-LR has a sweet high performance antenna and is a great little product (as opposed to the first gen UAP-LR). The LR also does 3x3:3 on 2.4GHz which is nice. The UAP-AC-PRO does 3x3:3 on both bands, 802.3at PoE and a second ethernet port. Personally I think it is a shame that the PRO doesn't support yet more streams.

The new APs promise a spectrum analysis feature through the remote controller and this is a real game changer for me. I have (beta) samples of these which I've been testing and so far they have been solid.

Also, 24V Passive PoE - this is common for WISPs and something you will also find on Mikrotik gear. Still, they should really get with the program and put their indoor stuff on 802.3af/at.