[davidajackson]

Without all the details here, but my gut feeling is this a bad offer, here's why:

Problem 1: >The offer is based solely on milestone deliverables, and will vest when those are complete

This is a classic way to continue delaying giving equity/increasing comp. There's always more to build to deliver features -- 'Sorry, but the app UI doesn't work on certain newer iPhone models yet, you don't get your raise/equity/whatever was promised until that's fixed...', and then something else after ('Sorry, we've had other people join the team and contribute to those milestones, we need to rework your equity model'). Not saying all these are legally possible but I've seen stuff like this done. Time based vesting avoids this.

Problem 2: You have 0 diversification. That's fine if you have the cofounder potential upside but doesn't sound like you do. Why not start your own startup? You are investing all your time into an illiquid, high risk company, why aren't you a cofounder?