I worked there in 05-06.
It's not the type of place you want to go if you're established and looking for the best deal.
It's the perfect place to go to get started from scratch. They pay you a 2k/mo draw, teach you for a few weeks, and sit you down with a successful trader as his apprentice. From there, it's up to you.
As has been stated, the contract is pretty clear about the money they hold back. As I understood it, the main reason they did it that way was because successful traders were given as much buying power as their trading success would allow - several guys trading GOOG had several million in leverage. And they never put up a dime to get it. So they kept that 20% to put it in the bank as leverage for the giant buying power they were giving people.
That alone isn't that unreasonable. That they were never flexible on this even with people who had been there for a long time with excellent track records is another conversation entirely. Obviously, I was never good enough to have to worry about any of this. (Then again, I was told of a guy who had been established and successful, then got screwed by some busted trades that cost him well into the 6 figures, and never recovered. I suppose they have to protect themselves from losses like that.)
Anyway, there are probably dozens of places that will give you a better deal as an established trader. But as a place to go get started, if you have the ability to live off a tiny draw, it's great. I scratched along for over 9 months, which cost them over 20 grand, and I didn't owe a cent when I left. (The only real problem is that I'm apparently blocked from trading with Assent now) Even though I was let go suddenly, after being promised more time (I was finally starting to get it together), I have nothing but good things to say about the place. Mostly I'm just upset with myself for not being able to capitalize on the great opportunity they gave me.
That said, I know nothing of the new Tower Hill model. It does sound like it's not as friendly to the new guy. Still, worth checking out if you have the time and desire to learn but no cash to put up.