This sounds like a great way to end up paying short-term capital gains tax on a liquidity event.  Why give an additional 15% or so of your money to the government?  Get your stock up front, file an 83(b) election with the IRS, and subject the founders to reverse vesting -- a buyback right in the event the founder leaves that gradually expires over time.  That way you own the securities immediately and long-term capital gains rates kick in after a year.