Dude if UE makes me a millie I would happily hand them 5% for it, considering that would be all I owe them, ever. Especially for all the free assets they provide.
Agreed. It's a very good model for building their customer relationship. I would be happy to give them 50k. It is revenues however, not profit. This might not look as favorable if you're running a moderately sized studio with payroll costs.