I use my I phone 6 as a dashcam with iOnRoad software which you can purchase from the Apple App Store. I believe the software is under 10 bucks and the video quality is excellant. It also provides you with real time speed information as well as distance to the vehicle in front of you and alerts you if your following too closely based on your speed or if you veer from your lane inadvertantly. I also noticed it will chirp if you approach a pedestrian or motorcyle. The con to this setup is while recording you cannot have full view of your maps ie: Google Maps. You can still receive voice commands and pop ups for turns but not the full map while recording via iOnRoad.
A suggestion might be to load the software on a retired phone and use it exclusively for recording leaving your phone for navigating and testing or calls when you are stopped
. Just a thought allows you to use what you already have instead of purchasing another device...
D