The 70Mai has a few quirks and issues to work through to get it going. It is the cheapest dashcam I can recommend as it's reliable with good video, but being battery-equipped it's not for hot climates. The B1W has supercaps, and is a better cam overall and a better value for the money even with it's slightly lower vid quality. Trying to go cheaper than these will almost certainly disappoint you. You don't get what you don't pay for!
Phil