I have/had a system on there but gave up because the trade interface is kinda klunky and awkward and still had some bugs in it. I agree, the fills aren't entirely accurate, because they (like all simulations) don't account for the cue (where you are in the place of the line of orders) and the size impacts on the market, and some other things. However, having said that, you probably aren't going to trade size that matters, or have to worry too much about the cue when you are starting out. The interface improves at a good pace, and Matthew is a good guy who works hard at making it a great product.
All in all I'd say that it depends where you are in the learning process... It may be a good place to start, but as the budda guy said, you really need to figure that out for yourself.
- The New Guy