The catch seems to be stamina, though it's pretty well hidden at the start. You get 1 stamina every 2 minutes, clearing one wave of one stage is 10 stamina, the stages right outside the starting area have like 14-15 waves (and I'm guessing it increases at higher levels). That's like 5 hours of stamina regen to do one stage. You also have to save some stamina so you can start a crafting project before logging off because they quickly start to take like an hour and you can't play while waiting for a crafting task to finish.

The instant travel times are a factor of the VIP level you start with, free fast travel for travel times under 120 seconds. I have a feeling there is no free fast travel once VIP wears off. Likewise VIP level also controls stamina cap and the amount of free stamina you get per day, I'm guessing without VIP its 300 cap and 300 free stamina once per day. So that's like 4 stages per day, tops, with a little leftover for a crafting task.

It kind of seems like a decent game at the start, but I having a feeling it will all fall apart once the VIP wears off and all the early bonuses go away or become obsolete.