I'm getting ATX installed right now, coincidentally
I was impressed by the demo. This is my first paid script. I've been using AT Lite for a few months now. The guy who writes it was kind enough to give me access to one of his sites so I could see it in action and I was very impressed.
I've heard it stacks up well to TM3 .. but again, I've never used TM3 so I don't know.
As for growing your site .. I think the trade script you chose is important feature-wise .. but ultimately how fast you grow comes down mostly to who you trade with, how you manage your trades and the overall design of your site (design being what users can click on, how much is skimmed etc.)