I have dashcams in all of my cars.
Being a poor pensioner, I was driven by price above (most) other features - but they had to do the basics to a suitable level.
Now, it is over 4 years since I bought the last one, so I'm sure that things have moved on a hell of a lot, but the features I wanted/needed were:-
Camera resolution of 1080p (I expect they are all pretty much 4K now) - to give a good compromise between clarity and file size.
The ability to record on a micro-SD card
The ability to review footage onscreen on the device
The ability to constantly over-write files, but retain footage if required
Have the ability to record (clearly!) number plates in all lighting/weather conditions
The ability to store satnav info on the files (giving location, speed, direction) which can be viewed on a laptop program (as Jonathan alludes to in his reply).
Now, I'm pretty sure that they will all do those things (and more) these days. I didn't need the ability to view the footage on my mobile by way of bluetooth (although 2 of mine have that function), or to operate it through an "App".
The one in the Elan was an ebay purchase which cost me about £30. The one in the VW came from Amazon for about the same price, The ones in the corsa were a bit more, but has 2 channels (front and rear).
All are wired to record as soon as the ignition goes live, or the car is struck (movement sensor).... and I've never needed any recordings for 'proper' purposes, other than it was nice to watch the parade lap at Brands Hatch on the laptop, with it all being mapped out and speeds shown on screen
