I have one and love some aspects - mine is a "Friday afternoon tent" though so not the ideal example! But I would still not go back to poles.
In terms of size and layout, the same applies as a poled tent - you probably already know what works for you.
They are easy to inflate and super easy to deflate
My biggest piece of advice would be to watch the weight and the pack size. I used to separate my poles and tent coz I am a wimp; and you wont have that option!
Some of the big airbeams are a 30 to 50 kg which - even if they have wheeled bags (and not all do) - you still have to man (or woman) handle into and out of the car etc, etc.
Just typed all of this and realised the OP was from 2014 ...........
Dont know about the Gelert - there are lots of camping groups on FB though...