[Sohcahtoa82]

Definitely get one. You can get one for under $100 these days, some even under $50. The quality starts to drop at that price point, but they'll be good enough to establish fault in a crash.

They're super easy to use. They constantly write in a loop, deleting old footage to make room for new footage as the memory card fills up, so you don't have to maintain them. And they'll usually have a button to press that will move the last couple minutes of video to a location where it won't automatically get deleted when full.