Check out the Drift Ghost X and other Drift cameras. I bought a Ghost X in early September 2019 to replace an aging Ion Speed Pro that wouldn't hold a charge. I liked the Ghost X so well I bought another in December. I usually mount them front and rear on my road bikes, although occasionally I'll use one on the helmet, mostly for casual rides on my hybrid.
Both were discounted around 25% from the list price, under different promotions. I think I paid around $80 for the first, $75 for the second after the Amazon discounts.
Helmet mounts using 3M VRB adhesive were included but those are primarily intended for motorcycle helmets. I bought clamp-on mounts separately for the handlebar/stem and seat post. Due to an old neck injury I can't take much weight on a helmet, although it's not bad mounted on my POC Omne Air Spin commuter type helmet when I'm sitting more upright on the hybrid. I couldn't find a comfortable balance point to minimize neck stress on my road bikes, so I switched to mounting on the bikes. The camera weighs only 120g but that's uncomfortable for me unless it's balanced properly, which is difficult to do on some helmets. I had to skip the 3M VRB tape on my POC and used Blu Tack gum or Scotch mounting putty to build up a mounting spot over a vent in the helmet. Bit of a kludge but secure.
They run 5 hours with the standard battery, up to 8 with the optional larger battery pack.
I usually set it to car DVR mode, 5 minute segments that loop continuously. Eventually it will overwrite the earliest files. With a 32GB card that works out to three of my usual rides before it begins overwriting. There's also a tagging mode to set a reminder for a particular video, but using that in traffic would require having a free hand and being conscious to use it. DVR mode is hands free. A 5 minute segment length seems reasonable for quickly finding a particular incident and saving it without editing (even cropping might discount the value of a video in a legal action) or saving an entire hour long video.
The included screen is tiny and strictly utilitarian for setting up the camera via a menu. It's easier to use the app, which is quite good. I've used the app and review screen on my phone to demonstrate a hazardous driving incident to a local school bus supervisor when a bus driver nearly clobbered me. That's very handy.
It's weather resistant. No problems in the two or three rains I've been caught in.
The lens (probably the sensor itself) rotates to accommodate any mounting position. Much better than my other portable video cameras.
No in-camera stabilizer. It's pretty stable mounted securely on the frame. Drift recommends helmet mounting but my videos were much harder to watch from that vantage point. (I also have a GoPro knockoff with good in-camera stabilization but that's one of the few good things about it. Otherwise it's not a good bicycling camera for traffic documentation.)
No accident detection, etc.
Video quality is good, a reasonable compromise of contrast and saturation in standard mode. Up to 1080p, frame rate up to 60 in 720p (there's also a 4K version that costs more). Better dynamic range for high contrast nighttime scenarios. But nothing will reliably record US license plates at night -- they're too small and highly reflective. And at night the slower shutter speed invariably blurs most frames. I'd be lucky to capture even a partial plate. But the vehicles themselves are recorded in adequate detail even at night. Far better than my Ion Speed Pro, which was good in daylight but almost useless at night.