I have to agree with cloverleaf in respect of his view of armex, theyr'e crap, I say that based on my own experience with them based on the use of a walther rifle which I got rid of in the end.
Although I have never had an AR20, I have several guns including Air Arms S200, it is accurate and cheap but spoiled by having only the small sized cylinder available, this means that power curve needs to be well learned as well as hold over and hold under so would not get my reccomendation. I also have a HW 100 and a Daystate MK3, I prefer the daystate for sport shooting as it is superbly accurate and very well balanced but I am not convinced that the electronics should go out in the rain.
So if I was to go out and shoot competition right now, I would by default have to use my HW100, it's very accurate, very rugged and easy to work on, it's also regulated so no power curve to remember.
I do at some point though want a better rifle for HFT though but I am struggling to find a genuine alternative to one of the Air Arms (MPR or HFT 900) or the Steyr. Based on accuracy and reliability.