So, what do they offer?
- Tutorials/community? Ubiquitous and free anyway, no value added.
- Analytics? Useless to everyone not doing highly targeted design (read: social games)
- Art? Well, as per the above, the devs pay for it anyway.
- Fit and finish? Now this is actually worth something. But all game devs should develop this skill anyway, and if you're a teenager learning game development, that's a good time to learn.
- Networking libraries? Could be useful.
The overall package might be worth something, but probably not worth having another finger in the revenue/IP pie. I say IP because, what happens if you publish game XYZ with them, independently iterate on the concept, and self-publish XYZ 2? Better to just own your work outright.