Frankly, I can't imagine why anyone would trade with a platform like Prophettrader, though I suppose there might be something I'm missing here ( wouldn't be the first time). Still, $9.95 + Exchange fees + $5 for Limit Orders!? And a fully penny a share extra for listed stocks? If I understand the schedule correctly, if I place a market order for 1000 shares of a Nasdaq stock, and it gets routed through ARCA, then I pay 13.95. If I use a limit order, then that's $18.95. That would be totally non-competitive...
Even if you trade size and never scale in and out (and thus prefer a ticket charge to per-share pricing), and/or really love their order entry platform, then I still can't imagine why you wouldn't try one of the RealTick brokers or Cybertrader - whose platforms are similar but offer a wider range of features, and which generally offer at least equivalent, mostly superior commissions and fees structures. If you like to get short, you might also want to check their clearing arrangement: Cyber was OK on that score, but iffy at times. It also offered outstanding customer service and support.
I'm a happy Tradestation user, even something of a junkie for their set-up, though I won't go into the various comparisons that have been the subject of extensive discussion elsewhere on this site. Other alternatives include E-Signal with integrated order entry from some brokers, as well as several others that have their advocate on this site.
If you're still interested in Prophet after taking a good look at the atlernatives, call 'em up (would also be a good test of their customer service) and get the fees broken down for the kind of trades you intend to make, and be sure you understand all of the details, then ask the same questions from at least a couple of other candidates. You might very well be able negotiate a better arrangement from whomever you end up going with.