As a follow-up to my suggestion...
Because they are quite popular, and ridiculously overpriced, they are also a popular item to steal. With the quick adjustment knob installed, it only takes seconds to remove a mount and arm. They sell an adjustment setup "lock" that takes a "Key" to turn it.
I replaced the quick adjustment knob with a regular nut on the items that I leave permanently on the bike. Not only is my phone mount using the ram ball setup, but my TomTom Rider 550 GPS (happily recommend despite it's few quirks) has a ram mount system mount. These items stay on my bike, so I use a regular nut instead of the quick adjuster. I have them just loose enough that I can move them with a bit of resistance to adjust for sun washout if needed, but tight enough so that they don't move while riding. They will sometimes move if I hit a large bump, but not under normal circumstances.
Here are the ram mount "securing" items...
https://www.amazon.com/RAM-MOUNTS-RA...0699862&sr=8-3
https://www.amazon.com/Mount-Locking...0699988&sr=8-2
Like I said...a simple nut works for me. If they want to steal it, I make them work a little harder for it, without spending $70