I went to Gundog Supply Company and was ready to throw down $189.95 for the Alfa .22, which seemed to be the top-of-the-line. I talked to one of the guys at GDS, who concluded that the Viper ($89.95) was enough for an occasional trainer like me. The Viper shoots .22 crimps (or shorts), which are a little shorter than a normal .22 blank. Viper recommends against using so-called acorn blanks, which are shorter still, and which can be difficult to extract after firing.
I use the gun in water training and in hunt tests. We shoot the blank gun instead of the shotgun for all of the dogs at a HT. It gets a pretty good workout on those days. Otherwise, in general training, there are maybe 2 shots per dog on a Sunday training day.
The Viper has enough heft that it does not seem likely to fall apart in your hand the way some of the really cheap guns do.