Many of my friend from facebook tried the game and then quit before reaching level 20. They also complain that it is very hard to reach 5star (Honestly I dont know why would they felt that way).
Depends on their personalities IMHO. It took me 2 weeks of play until I decided to invite my RL friends to play. And after I fully understand the game system, I only invited the two that are patient type while not asking other friends with impatient personality. One quit due to heavy workload hit him before he got hooked up to the game. The other remains and enjoys the game. He has time to raise his young baby, work and still be able to enjoy the game. In the end, no pressure playstyle can enjoy the game as f2p or even being casual spenders while impatient playstyle will be tempted by the slowness of the game and feel they neeed to spend to be better or to be competitive. That's pretty much of it