I'll clarify: 15% of all contract programming revenue. As I'm a contract programmer, that's all of my revenue. But they did say they won't take a fee on your day job if you have one. They told me their average project is 1 - 2 months. That's from them, not me. Maybe you've been lucky. But if you're not giving them 15% of your contract development revenue then you may want to review your contract: you either got a special deal or you're in breach of contract. They even take their fee on any equity you're awarded.
I'm one of the developers Mr. Altman is talking about and have recently rejected an offer from 10x. I have to agree with Mr. Altman's point of view: I'm making 1.5 - 2.0 times the average developer's salary already. Speaking with 10x, they told me that their average project was just 1 - 2 months long and that I should treat their service as a supplement to my income rather than relying on them to keep me booked.
The problem is they charge 15% of ALL of my income for that privilege and don't make any guarantees. Why should I pay them over $2k a month for them to possibly make me new sales when I'm already capable of keeping myself booked the majority of the time?
The whole thing reeked of predation to me. If they're really able to provide more value than they take from me, then they should only be charging me a commission on the sales they bring in.