A few notes:
Got 17 phones running. Have about 5 “nonessential” ones off to the side that I haven’t deployed yet (additional phones that I didn’t have before since the price of $10/seat/month seemed way more than $200 once). Have my old phone tree up with all the same extensions.

Some initial notes:
1) phones sometimes do OK if they’re on a different subnet than the controller for initial adoption but usually can’t be seen by the controller. Otherwise, they’re easy to adopt. No Talk app, but the web console makes for easy adoption on mobile. The phones identify themselves by their MAC final 4 digits, and they prominently display them until they’re adopted. I went with an “adopt in place” strategy and went one at a time (so I knew which user to assign the one new phone to). As easy as adopting a new AP/Switch/camera as far as the Unifi suite goes.
2) users may only be assigned to one phone. Each phone may have one user. You can get around this with ring groups (medical clinic. There’s a nurse who basically stands all day at one location with a phone but sits at another to start the day, at lunch, and around quitting time). It’s easy to make a ring group with her two phones and make them always both ring (either simultaneous or in sequence). Voicemail can only go to one of them (easy, she checks voicemail at one of them already). I haven’t gone through adding them as limited users to check voicemails on the web and am not sure if I will or not. I’m also not sure if the emailed voicemail is a good feature for us (loaded with protected health information, and I can’t control Unifi’s security standards or force encryption).
3) it’s very easy to set up an auto-attendant on desktop. Unfortunately, tweaking this feature on mobile is not good on iOS in safari (haven’t checked with others yet. And yes. Shame on me for using an iPhone. But that’s another story for another day). But as far as the attendant goes, it’s a wizard. It asks first if it will operate differently based on hours then has a GUI for a week where you click/drag the schedule around. It’s intuitive, but there’s no way to copy Monday’s schedule through Friday (as most would probably do). It’s a one-time thing, so it’s not really worth requesting change or expecting change for it, but I noticed it and was slightly annoyed. The wizard gets a little silly here. It allows you to make 3 actions on the tree and that’s it (then lets you add more later). It doesn’t trigger you to act how it should act in the “off hours” segments, so I started making a second attendant before realizing this. Anyway, the features are nice enough. Ringing a group or user, then an action based on them not picking up (more rings, certain voicemails, etc). If you’re like me and have a 3rd party answering service, do yourself a favor and add them as a “Global Contact” before you start setting up your attendant. But you can have your attendant ring an extension, then another, then an external number if that’s you’re workflow.
4) there are no good videos of the workflow on a Touch Max vs Touch phone. I bought all Touches because the girls agreed the desk real estate was more valuable than a bigger screen. Maybe this next part is different on a Max, but I’ve seen nothing to support it. On most traditional copper/VOIP PBX, you have a few “lines” where someone is on hold. So you buzz and say “hey, pick up Line x.” And the user can see line x is red, so they pick it up. On the Touch phones, you can put a call on hold OR park it. But there’s not a great way to manage multiple calls on hold. When multiple calls are parked, they’re handled by caller ID. Unfortunately, the current caller ID is the 10-digit number unless it appears in your global contacts. So if you have 10,000 patients who may be calling, and you haven’t entered them into the ID, you get no ID. And the workflow will have to change from “hey, pick up Line X” to “pick up ‘xxxx.’”
5) I haven’t really done this yet, but seems like the current way to treat a Holiday is to create a new smart attendant and manually switch which one answers on those days. Or to adjust your schedule up to a week ahead of time and manually adjust it back afterwards.

We did a little bit of “bombarding” one user to see how these features worked. I’ll probably constantly tweak the attendant, but I’ll get the receptionists playing with it next week and used to answering/transferring. Assuming I get their blessing (ie- no red flags), I’ll start the porting process (current provider asks for 30d notice).