Just to add my twopennth.
I picked up a 4 month old AR for under £400.
Mods done ...... Shroud milled off but ONLY so I could fit the UK Neil airstripper that I picked up on evil bay. Changed the trigger blade for one from Maestro , it has more adjustment than the standard one .
I have 3 FT guns in total , HW101 in a custom GinB stock, ProTarget Mk 3 and the AR . It's the AR that I use in preference to the others.
As said earlier they have a fairly quick lock time and being modular easily adaptable.
Agree with Rich as well don't fill them above 200 bar even though the cylinder will take 300. 200 bar will easily give you 100 shots should you need .
Barrel is 16mm and accurate again as stated above.