Mike,
I had to laugh as I just sat down this morning to look for the very same thing as my son is shooting a TriStar Viper G2 in the 20 Ga too.
I just ordered one of each of the TS shell catcher (TS-AL2) and the Birchwood. I am hoping the TS works as I can use the Birchwood on another gun.
I can let you know what the outcome is once we have tested them out.
Jon