It's very dependent on your budget. The YI Smart is £50 and we'd argue it's one of the best budget dash cameras around. Review here: kit.honestjohn.co.uk/reviews/review-yi-smart-dash-.../

For something with more features, the Garmin 55 is great: kit.honestjohn.co.uk/reviews/review-garmin-55/

A dual dash cam is a good idea if you're worried about someone running into the back of you. Generally, the insurer will find the person behind at fault because drivers should leave adequate braking distance, but for 50/50 liability situations or where you think the other driver was tailgating, texting, driving dangerously etc - a rear camera can capture important footage to back up a claim. Our Nextbase 512GW and rear cam review is here: kit.honestjohn.co.uk/reviews/review-nextbase-512gw.../