I have a bit of a unique insight as to how these places operate. I am on both ends at the moment, being funded by a couple of FX 'firms', and also contributing to the material for a couple of other ones. I can assure you this is about handing fees from the entries to the very small percentage of winners. There is no money, other than the entries.
To start out, these companies will have a certain amount of a buffer backing them, but in the end they know that less than 3 percent are going to keep an account for any serious amount of time. The most common thing for the 'successful trader' is to get 'funding', and them blow up almost right away.
The worst are the companies that put a time limit on your combine, and expect ridiculous returns. The common set up at the moment is 8-10% in 30 days, followed by 5% in the next 60 (or less). This trains the monkey to get aggressive once he/she is funded. This is especially true if they have failed several times, gotta get that money back for all those losses!
There is a way to make money, but with all things, it takes time. First of all, if there is a time limit to the hamster wheel - that's an immediate no. Secondly, one stage is what you want. Also, you should be able to withdraw smaller amounts. (Some make you earn 10% before being able to do so.)
The only way I have seen work is to have several accounts, generating small mounts every month. Furthermore, you aren't a problem for the company. If you earn too much, that's going to be a problem. It's much easier to pull $300/month from 6 accounts than it is to pull $1800 monthly from one of these firms.
Also, always take a look at their addresses on websites. You run a search of that address, and viola! - you will find those are almost always office sharing buildings, many that offer 'virtual offices.'
Again, you can make money, but its a slow and steady process. You won't be retiring anytime soon.