re: Poker & PokerStars' Spin and go
Well, its not much bigger money for PS. The rake is even public on their site, its 7% for low stakes to 4% at highest Spin & Go.
There is no common rake, its just difference between money collected and paid out in 100k tournaments (if prize pools are exactly according probability, its not clear to me, if prize pool is really random, or those numbers are exact per 100k tournaments. Of course in long term it should be the same).
What is different its much close to gambling. Even if you are beating the format, your profit will be much more depending on luck then other formats. So you need much-much more tournaments to be sure about your edge.
Possible advantage is that there will be tons of weak players.