It’s a fail from me too. All my birds are not maxed out, and I found it was just a rehash of earlier screens I recall playing and not enjoying. After about 20 attempts, I only made it to the boss pig once and got a look at the level, before I promptly wiped out and was presented with the “Buy In” to finish with gems.
Granted, if you look at it this way, you could buy in, finish the level and get the prize- which today was 100 yellow feathers, 100 grey feathers, a treasure box and chili spell- well worth over more than 60 gems if you spent only once- but that’s provided you even succeed. It would be your choice.
Frankly it’s just one more attempt to get you to use up your gems and have to end up buying more eventually.