It is not, which is unfortunate. Though you can sideload the APK directly from github and at least avoid the Google Play Store. It is also ad free, which is the primary complaint I have currently with Sync (yes those can be removed, but for a relatively hefty $20).
Sync is the only one to actually give a smooth experience. The rest have loads of usability issues. I haven't used Summit yet though. I thought I tried all of the various clients by now.