Have you ever tried to send more than one attachment in one email from productivity application (like for example Pages)? It is impossible without this app.
Now you can just export documents as usual from any application, using option "open in..." and select Attachments from apps list. Then again and again... and when your attachment list is complete, then simply tap send and you've got classic email sheet with all listed attachments added.
Just works. Without any accounts, without logging into any email (it uses iOS accounts), without sharing anything to cloud services, without problems and headache about sending more than one attachment!
