My take so far is that this (the H3) is a viable integrated gimbal solution that works. I would put the M5 in that category, of course (though I have not personally put it in the air yet). Also in that category is the DJI Zenmuse series, but this option is limited by single camera/lens choice in each gimbal offering. Going further, the latest phantoms and the Inspire are great but also have their limitations.
The Gremsy software is very easy to use. They offer nice mounting hardware solutions. And their support is very good (over on Facebook, which is not my preferred choice, but they are responsive there).
The H3 is a perfect size for flying small cameras (GH4, Sony A7, BMPCC, the Blackmagic micro if they ever release it, etc.). With the A7Rii, loxia 35mm lens, battery, etc. (all up weight) the H3 and camera/lens come in at 4 pounds 6 ounces. That excludes a few ounces for the quick release and mount on the copter, but the bottom line is that this is about as light as it gets. All-up (with 21000 mAh battery) my S1000 is almost exactly 9kg.