I think the number one piece of advice I can give anyone is watch your attitude. Nobody likes to work with a know-it-all especially one who is wrong.
Clear line of site is an absolute must. I personally wouldn't want a Rocket Dish in a tree - too much wind load but YMMV.
568B is the standard for PoE not 568A.
I would also consider it normal for the installer or company to change the IP and password of the client radio. If they didn't any customer could log into the antenna and grab all the connection and security setting info.
Judging by the reviews I believe they look like a reputable company. I do not have any affiliation or contact with them. I'm just basing what I say on what I read.
You're confusing 568-B with T568B. One is an IEEE standard, the other is a cable termination. Many people use 568A termination for POE for the same reason they use red tape on the ends of crossover cables; so you'll know which is which.
FWIW, there is no official standard for PoE termination. It's just good practice.
And Etheric have quite a few antenna in redwood trees. You should ask them about it. I don't like the idea myself and if they'd suggested it from the get go I'd have ash canned the entire project before it got off the runway. I live in an area with sustained 110 mph winds every Jan-Feb. Ever watch a 200' redwood bend over and touch its toes? I have.
There really isn't any sensitive network data on an M5 and I would estimate that any provider using Ubiquiti equipment does MAC filtering to prevent malicious users. God help them if they depend on WEP.
Good comments on attitude. Mine needs improvement right now.