They are a very solid choice no matter what any of the haters say. Of the mech autocockers available from WGP these days there is really no diffrence between a trilly and a prostock. Prostocks have the advantage of being more easily upgraded as there is a wider range of parts available for them, but Trillys can be upgraded just as much and the two guns shoot identically.
Don't waste your money on the SF versions. You're paying a lot more for just a shorter trigger pull, not faster balls per second.
Don't buy the Sport series, it just doesn't have enough goodies for the price it costs. The comp is my favorite as I like the coloring and unlike most, I actually like the trigger frame. The pro is the most loaded, it comes with a second barrel back to help you with paint to barrel matches, which is a great plus. If you have the cash, go with a pro...unless you really don't like the way it looks like me.
You should know before hand that autocockers require timing and you need to learn how to do that. Also, they rely very heavily on a good paint to barrel match to stop balls from just rolling out of the barrel since the detent is only there to prevent double feeds. Don't short stroke, you need to complete a full trigger pull and release everytime you squeeze or you'll double feed the gun.
Do your homework before you buy it and save yourself some future headaches, my favorite sources for info: