I too got one of these without the scope. Cannot fault it in any way ,so far, it's stupidly accurate and the trigger is predictable.
I was advised by those inthe know about the regs used ( it uses a twin regulator set up apparently) NOT to fill it above 250 bar as it is possible for the reg to 'lock' up ???? as my bottle is only rated at 232 bar then no issue. For a typical 30 shot course I fill to 200 bar and will finish on 150 still well within the 'green section' of the manometer so more than enough shots @ a 200 bar fill.
I like the fact that it is 'modular' in it's design so that you can quite easily adapt / customise it to suit you.
Coming from the Walther stable there are parts from the Dominator Alutec that will fit directly e.g. the wooden grip if the plastic one is not to your liking.
These were slow to sell to start with and that may have been due to the fact that they were priced as low as they were, people just thought that they could not be as good as that for that price.
Gary Chillingford has done a small piece in one of the mags a couple of months back estolling the virtures of the AR20 and says as much in his article.
When they first came out the main two critisims were (a) They were front heavy, and (b) A POI shift if you rested the front of the shroud .
So if you find that it is front heavy you can get an ali cylinder from Walther for it or get an aftermarket one made, there are a couple of people doingthese now in Titanium. As to any POI shift I can honesty say that mine has never had an issue with this and I know of another AR user who also has not experienced any POI shift either.