Mailbox was already pretty great to begin with, but it's about to get even better. The (arguably) be-all and end-all Gmail app for iOS has just hit the ripe age of 1.5, and has received a fair number of improvements.
Chief among them is the ability for you to use Cloud Search to search through all your messages. Account-specific signatures have also been included, as well as the option to open links directly in Chrome. And, of course, the standard bug fixes and such that come with all updates.
If you haven't been using Mailbox, now is certainly not a bad time to start!