Hm, so it's a 3% rate on 3*s, and Superhippo is involved. Can't say I don't have a bad feeling about this. Guess it depends on how generous they are with currency and tickets, or what the rarities of event girls are.

Good news is that it looks like it'd be an insanely fast reroll if you wanted to try and secure two 3* girls (one from guaranteed, other along the way) using the tutorial missions to fund the step up - Of course, you'd lose your prereg rewards. I can't even remember what they were.