Occasionally, fanatical TV viewers will try to get together and pledge enough money to produce another season of their favorite cancelled TV show. In return for that money, they get to see another season of their favorite cancelled TV show (well, they would if the networks were smart enough to work that way).
So if I donated $5 to this startup and got a life membership with like 3 fighting dudes, while they charge $1/mo post-launch with the same plan, I'd call that a pretty fair bargain. Of course, I don't quite know the legality of selling a chance to possibly in the future own a product that isn't developed yet and might not ever exist, but at a discounted rate.
The idea behind many huge movements today is to be a part of something. If you take a risk to donate $5, you could potentially lose it yes, but you could also say that you helped launch something big.
If you don't have to give up equity then why opt-in to do it? If enough people believe in an idea/want it built then it's a fine way to make the money that you need. From the sounds of it they've made it this far in a year with almost no funding so imagine what $20k could do...
Also, I believe Diaspora was asking for $10k and simply had an idea, at least this team has executed.