UA's API for push notifications is best described as the API Apple should have provided for APNS. At first blush, it doesn't seem to add a lot of functionality -- but once you spend some time with the API, you realize that the UA folks put a lot of engineering effort into making your life easy. Feedback service? Much easier. Push to a group of devices? Yes. Device tagging? Yes. Scalability? Not your problem. Easy-to-use control panel for debugging during development? Yes. Getting started with UA literally took me all of five minutes from installation of the python UA client library to first device registered & notification sent.
Given how little they cost (recently lowered prices, too) and how much potential headache they take off your plate, I would warmly recommend them. I briefly considered a "build-it-myself" approach, but scalability questions made it an easy decision. The first 250k messages are free (IIRC), and if you get to the point where you are actually sending a million messages a month -- you probably have enough revenue to cover the $1-2k in UA fees. There's no contract, so there's nothing preventing you from DIY when it makes financial sense to leave UA.
To top it all off, the UA team is friendly and responsive.
I haven't used their in-app purchase framework yet, so I can't speak to that.
Hope this helps!
Without a moment of hesitation, I would strongly recommend choosing them over rolling your own. They're great guys, know what they're doing, and are having fun doing it.