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This is a clear explaination of the value for each type of user. The frontpage of the app isn't as clear with the value prop. Put this on the frontpage in 3 big clear points. Great idea overall.
Why compare it to 99designs? I don't see any resemblance and you're almost hurting yourself with this comparison. "Crowdsourcing" may be a better word choice. But you're asking for a "bid" instead of actual work, so it isn't even technically crowdsourcing.