Don't overlook the CME fees for data (starting at $85 per month) and the fact that TST's Combine-fees, which start at $95 per month, include those fees. If you have the capital to fund your own account, then you're not part of TST's target market anyway, are you?
I thought it was only $5 (it must have increased since I looked). Meanwhile, if you're not a trader at all, it's zero. But neither of these figures is relevant to this context. What is relevant is that the CME $85 fee is already included in the TST fees (which start at only $95), a fact of which many people implicitly criticizing the Combine-fees seem to be unaware.
Yeah it starts at 5 and the "combo meal" is 15. Yes I agree with you, if you trade multiple markets it brings the min combine down to 70, which ain't bad for the opportunity it can bring.
That's true, however, you'll find that trading in your own simulator vs. TST is quite different, since you can "cheat" in the broker's platform whereas with TST you have to follow a strict set of rules.
When comparing costs, compare the data fees for a retail vs. TST. Retail with AMP, for example, is $15 for the bundle (data fees). TST charges $85 per exchange. The combine includes the data, the live account does not. So if you want an "apples to apples" comparison, it's $15 vs. $85 for CME data fees for live accounts. Platform costs are extra, however I believe TST won't charge you extra if you use CTS (T4), which they include in the $85/month CME fee.
And that's per exchange, too! You could spend $340 per month in CME data fees alone at TST, whereas in my stand-alone, non-professional setup the equivalent is $15.75. For a small combine with a strategy spread over all 4 markets, that'd be a very expensive difference.