He mentions the availability of Mailbox as a useful third-party app. However the fact that Mailbox only works with proprietary services, being restricted to GM

He mentions the availability of Mailbox as a useful third-party app. However the fact that Mailbox only works with proprietary services, being restricted to GMail and iCloud, should send red flags, because this app is not provided by Google, but by Dropbox and personally I'm seeing a conflict of interest and given that it isn't based on standards, you can bet that it won't last. I also tried it out and I found it half-baked. This point was weird. It's because of Google's poor support for standards that I'm considering ditching Google Apps. Because GMail and Google Calendar are all fine only as long as you're using the official apps.