I'd just say this: our current business has sharply better cash flow than Matasano's did (Matasano also didn't require pre-payments, but it did work primarily with larger firms, where this business works exclusively with startups), and our business would not be possible with prepayment. I only see downsides to prepayment, and my bias is to assume the need for them comes from accepting clients you should be rejecting out of hand. But I concede that this may be a quirk of my own experience.