Costly. Youre always kept at a disadvantage. If you upgrade your plane, the game updates itself too so youre back to square one. Imagine your plane being 5 stars and needed 3 hits to be shot down then upgrading it to 10 stars only for the plane to be shot down with one hit! By the same opposing plane!!! Good game to pass the time but only to a certain level. Just don't bother with buying upgrades. Just watch the ads.