I tested this in their beta for Mac and am now back on Mail.app. After several updates, I continued to suffer from primarily two issues:

1. App would crash in the background and need to be reopened. 2. Emails that had been archived in Gmail still appeared as “incomplete” in Mail Pilot.

Perhaps the latter is product design and not a bug, but regardless, it was frustrating to say the least that emails I had hidden from view on Gmail were still visible in Mail Pilot.