Double entry means that you can keep track of more complicated situations with a less complicated interface than other apps.
This app seems on track to become the perfect iPhone accounting solution but is only almost there; it is missing some features I would like (particularly reconciling accounts) and the number of taps to do something isnt streamlined everywhere (in order to get from the history of an account to add an entry you need to back out of one thing and go into another.)
Cayennes about Ledger