Because you're entering expenses so regularly, usability efficiencies are really helpful - especially if you're entering half a dozen expenses or more at a time. At the moment, when entering an expense, you need to hit 'Save' - and then you need to separately hit 'Close' for every expense entered. This seems to be an extra repetitive step without any benefit, as it will be a rare use case where someone hits 'Save' on such a small form, and wants to remain on the form / doesn't want to add their next expense or move to their next task. It's a tiny thing of course, but when you're using it again and again it feels clunky - and I'd imagine a really easy fix for the Save button to also close the modal so you can move on to your next action/expense :) As a side note, the app iXpenseIt Pro have done an amazing job of making expense entries super efficient for users. Moxie of course does so much more than just expenses, but I thought it was worth mentioning the app as they've obviously spent a lot of time refining it as it is their core business - and it could be a useful reference :)
