Barebones; does the job well
A stable app that handles the basic PGP-encrypted email workflow is a godsend on iOS.
App has a bit of a learning curve, as most PGP-related software does. PGP/GPG is hard. Most users of the gnupg command line should be able to handle the export/import steps with ease. (Protip: when following the instructions, make sure you export in ASCII format and include the secret key before the public key.)
mtigas about
oPenGP