One of my primary design goal was something like that: "My mother should be able to use this tool to calculate/plan her vacation expenses". (My mother is older and not a tech guru you can guess :)) So the primary focus are on simple calculations with meaningful context and immediate feedback. Nothing fancy.

Though, beside that, I think it provides some nice features. E.g. the matrix creation/editing functionality was born because I could not find a simple tool to double check my rendering calculations with.