You've expressed much of my concern here, however, to add I wouldn't be responsible for building the entire app. In terms of coding my role would be limited to frontend dev. I'd also probably help make some decisions on app architecture and of course share my own ideas to in helping to shape the app as we're dealing with pretty loose specs.
to add I wouldn't be responsible for building the entire app
That does change it a bit, but you should still be in for or close to an even share if no one is going to pony up cash. You are taking the same risk as the rest of them.
I caught that vid too, but not sure how important the angel funding part is in this case. They're a small profitable shop working for a client and cutting him a break since he's a friend as well (we're all friends here! hah). So the client pays a smaller amount for the app that he plans to use for his own business but receives only 25% of any future profits that the app generates. The client's expertise is not sales, he runs a business in the domain and knows other small businesses with similar needs.
If it wasn't friends, then I would base my judgment solely upon my evaluation of the product's potential to be a success (given the people working on the project, and the idea itself). I know my friends, I know they're competent, and I know on a scale of 1 - 10 in terms of having an "in" I'd put the client at an 8. Those factors sort've take some of the risk away for me, but not quite enough to put me at ease and 10% does feel like a small amount to be working for.
I wouldn't resent my friends if the project fails, they're my friends. Plus resentment is one of the seven deadly sins of business.
