A percentage fee, or even a per-user fee, would push me to do it by myself. A bad login mechanism takes a couple of hours to be integrated. A well done one, cou

A percentage fee, or even a per-user fee, would push me to do it by myself. A bad login mechanism takes a couple of hours to be integrated. A well done one, could take maybe a week (very well done, 1 dev, extreme case), but a percentage fee for any kind of decent revenue would reach that same cost within a year. I see this working maybe for a single dev shop, but then you might prefer saving every cents you want. Paying a fixed fee might work, but if you start charging per single user, it's problematic. I can see some value if it's per bundle of users (e. G. Every 10 users the pricing increases)