Tried this out a little bit today and I'm pretty underwhelmed (played on my Android phone, but I doubt it's different on iOS).
The core game is fun, but the ads kinda kill it. Every ad seems to be a 30 second video WITH sound that you have to manually exit out of after it plays. And to make it worse, they play every time you restart a level an ad plays, and every time you finish a level an ad plays UNLESS you do all 3 optional objective in which case an ad wont play after finishing. It's a cute idea, but it's hard to get all three of the objectives done on the first playthrough (the 3rd or 4th level had some requirements I couldn't figure out how to do even after replaying 3 or 4 times).
I only played a few levels of the game, but the levels are pretty bite sized, so having to watch so many commercials was pretty annoying even after the few I played through.
There is a single IAP from what I can tell to remove ads and add extra content and features, but it was $5.50 which seems pretty high and it also seems to lock important stuff behind there like ranged units (but that might be for multiplayer or something).
The reviews I just read seem to indicate that the game gets unfairly hard after the tutorials levels, so I doubt I'd have wanted to spend money on the game even if it was more reasonably priced.
A shame, because I'm always looking for good RTS style games for mobile. Love good Tower Defense games like Kingdom Rush and Plants vs. Zombies, and more RTS style games like Eufloria. I'm hoping the Kingdom Rush developers next game is really good since it'll be more RTS style than Tower Defense.