The Zillertal Arena and slopes are actually very good, I just had a problem with a local board rental that I wanted to share...
Just returned from a week snowboarding and hired board from Sport 2000 in Gerlos (the shop near the Almhof). They have new Solomon bindings and the problem is that with snow and ice in them, they can slip and the boot can come out of the bindings! When I took it back there were two boys in front of me complaining about the same thing. The shop's response was firstly - its not their fault 'its the snow and ice' you need to stop getting snow and ice on the snowboard!, and then 'its the wrong type of snow', and finally all bindings do this (it has never happened to me in 10 years...).
I have been going to this shop for a number of years, and never had any problem, but am not impressed by their reaction when I did have a problem, which was denial and poor customer service. It seems they are happy to take the €100's, but not for any service when there is a problem.
Hope you have a better experience, but you have been warned!