www.aliexpress.com and search for OSMO... and be amazed how functional accessories can be.
What about a Universal mount which has TWO rosette mounts? No need for the stupid extention arm, you just can use your phone AND the mic-boom rail. And as added bonus, it has a 1/4" mount for tripods... Just as god meant it to be!
Take a good look DJI, innovation shifts outside your R&D department.
They also have a alternative to the Extension arm... so you can get that balance as well. When i'm filming, im holding the phone mount also. This is the most logical way to hold.
No that's why i posted the box with the contents. i had the Extension arm and Universal mount already. But alltogether it looks kind of sweet. The Universal mount could go, it's a bit overkill but you can hold it better there with your left hand.