I'm pretty sure they are managed by E-Processing services, the same as Colosseum and Old Samarai.
I just signed up there today to get free $10 no purchase. I'm waiting (impatiently) to get the $$ in my account. This operation lets you cash out as soon as your account balance gets over $50.
There are no wagering requirments, but blackjack is one of the excluded games.
Please note that I have cashed out (from the free $$$,WITHOUT making a deposit, at numerous MGS sites, all with video poker)
The best way to play bonuses like this IS to play video poker, and NOT TO PLAY FULL COIN (although normally I do advocate full coin play.)
Play 25cents at a time. Use the double up option as often as possible. The double up option has no house edge whatsoever. So as not to take too much risk, I'll usually double 3-4 times, and then collect. Then play the next hand and double again 3-4 times.
This way you can slowly but surely grind out a profit until you hit a decent hand like four of a kind or a straight flush (at jacks or better).
Before you know it, you hit the $50 cutoff, and cashout to paypal.