Why do you want to be a beta tester? Testing takes you away from what you normally do with Trainz, so you have less time for the things you normally want to do. You have to do ALL SORTS of scenarios, trial, tests etc., often possibly with different options and specifications and really have to abuse the version you are testing, often to the extreme. Like doing with the version you are testing what you normally would not do in or with the game.
This takes a lot of time and effort to do as you often repeat some of the ways you test over and over and over, often so, you really get sick of this after a while.
I have been a beta tester (not for Trainz) of a hugely successful game in the immediate past and after testing these different alphas, betas and up to the gold version for several months, I simply did not bother to open the final version of this game to play (which I received for free for doing the testing), as I knew EVERYTHING that needed to be known of it inside and out. Some of the time, you might not even test a complete game, only parts of it, depending which game this might be.
It sure takes away any surprises one normally has in opening a brand new unknown game for the first time to play.
My opinion
VinnyBarb