The only downside of a dashcam is it only captures what is in front. Sometimes I consider installing one looking backwards.
And a $30 cam is going to suck. I have a couple different $100 cams that are highly rated and the pq is acceptable even at 1080p.
They make ones that face both directions (has two cameras), and they make ones where you can place one in the rear like a backup cam (externally or internally, although you need to figure out power (some come with adhesive and a thing that lets you crimp onto existing power). I feel like there's other options
It'd be nice if car companies would integrate a dashcam, and/or standardize a cam holder so that you could just slot it in (and not have to route the power cable). Most of them that do have cams have a bunch of external ones which isn't quite the same as a dash cam in that it doesn't give you a great idea of what the driver was able to see.
I think there's an optional one on the Corvette as part of some track/performance package, and includes an SD card slot (that you can lock).