I'm really impressed with how well my newly acquired Osmo Mobile works with my iPhone 7 Plus. It handles the usual walking around very well as expected but I didn't expect it to work as well on my kayak. Especially since my prototype mounting isn't really sturdy enough for the Osmo Mobile. It works fine for my much lighter LG360 Cam.
The kayak has all sorts of complex movements to compensate for. Each paddle stroke causes some roll and heading change plus up and down and rolling movement from waves and a slight wobble in the mounting. The video all looks great! Video recorded on a fixed mounted video camera is completely unwatchable.
Of course I realize the Osmo Mobile is not waterproof so there is some risk involved but I wouldn't take it out if there was some danger of swamping. Likewise my other camera gear, GoPros and Olympus TG-4 excepted.
I'm still learning various settings about the Osmo Mobile. The roll calibration seems a bit vague and doesn't always come out level. I haven't figured out how to set exposure compensation for the DJI Go video cam. The edit feature is not very user friendly. You have to hunt all around to find things. It starts out in a crazy abbreviated movie clipped out of my latest video clips. Completely off the mark. Music blots out my recorded audio. Would like to shut that off. Automatic saving to the camera roll would be MUCH better. There needs to be some way to mount an external stereo mic for the iPhone 7 Plus. What's the point of better quality video with lousy audio? It's exceedingly difficult to overdub synchronized waves in a video where the iPhone mic is full of wind noise. I'm sure I'll figure these things out in time.  

Calidris, thank you for your support to DJI product, we are pleased to know you enjoy it.
For your questions, here is a brief guidance.
1.  The roll calibration seems a bit vague and doesn't always come out level.
The gimbal must be balanced before powering on.
2.I haven't figured out how to set exposure compensation for the DJI Go video cam
There is a yellow circle in the screen, where you can adjust the exposure.
3.Music blots out my recorded audio. Would like to shut that off
Music can be blocked, please check the screenshot below.

4. Automatic saving to the camera roll would be MUCH better
This function is not available, the footage is saved in APP automatically.
5.There needs to be some way to mount an external stereo mic for the iPhone 7 Plus.
The Mobile phone connects to Osmo Mobile via Bluetooth, so the external mic may hard be used, besides, the port of mix is blocked by gimbal.
6.What's the point of better quality video with lousy audio
The audio is recorded by your mobile phone, there is nothing can be done in DJI Go or Osmo Mobile, sorry for this.