Sky Gamblers: Storm Raiders free at 11:00 PM EST(first time a SG game has gone free?)

Been interested in checking this out for a little while, so it's hard to pass up free. Curious if it has multiplayer though?

 

Yep, it does.

 

So are all the additional planes unlocked only through IAP or can they be unlocked through regular play as well. Dont really have an issue with that since the game itself is free. But jut wondering.