I purchased the OSX and iOS versions a few months ago and am running the latest versions. The work flow is pretty nice, but:
Mac OSX: even the latest version is slow, crashes almost daily and does not always display a thread intuitively. Note that I have 4 gmail accounts configured.
iOS: This is the one that drives me crazy! Also slow, buggy, and its notification system is bonkers. I get notified if I send an email. If I send an email without a subject (usually I'm emailing an attachment), I get continuous notifications on my phone.
I had tried Mailbox and the only thing I did not like was that I could not use gmail labels (easily). The reality for me is, at work, I have a Windows PC and use the gmail web client interface, so I still label and 'star' emails.
Mail Pilot let me archive to folders (labels), but it's way too buggy, esp. the iOS version.
As of today, I am back to Mailbox and am awaiting their Mac client.
The Mac version of Mailbox is in currently is private beta and when released to the public, it will be free.