It does fit, but it can slip its heavy and hard to play while laying head up because the moga pro grip don't have a lock it might be the same issue with htc one alone. Although in the video it doesn't drop it does feel that it might, but it still fits which is the most important.
Here are more photos:
Connecting the moga pro to my phone seems to disconnect the wifi, not sure if this is a common issue. It is having hard time to find the controller with wifi on. Other than that everything seems smooth, the moga is very responsive.