If you think $10 is expensive for a calculator on iOS, rest assured that PCalc is a great value.
The calculator itself is highly functional and super customizable. One of the best things, however, is the developer behind this app, James Thomson. This man never stops - with every update to iOS, he always has updates to incorporate new iOS or iPhone features on day 1. And he doesnt even charge for updates. The man has been developing versions of this app for many years and wont likely stop soon - so youll definitely get your moneys worth if you invest in this app because youll still be using it years from now.
The one thing that I would like at some point, however, is the ability to enter full equations like you can on a modern graphic calculator, but alas, PCalc isnt that kind of calculator. For what it is, though, it is great.