Almost none of the camera's have a 2+ hr battery life. So if you really want a camera running continuously for a 4hr ride, you either need an external battery or a Fly12.
Yup. I've ridden a few times with the Ion Speed Pro and it gets just under 2 hours -- usually between 1:45 and 1:55, depending on temperature and whether I run it continuously or intermittently.
The other option is something like a GoPro Session that you can quickly turn on. For example, if you're being harassed by a driver.
Same with the Ion Speed Pro and similar Ion models. Very simple, no-look operation. Two buttons: a push-button, which is almost superfluous (mostly for taking still photos or turning the camera off rather than using standby); and a slider for record and stop. There's a palpable vibration (not very audible in most conditions) to indicate operations. It's weatherproof (Ion claims waterproof down to 30 feet), so you don't need to wrestle with a clumsy housing.
I may add an external USB battery pack for handlebar mounting, since I already use a pair of small pouches on the handlebar for holding my phone, P&S camera, etc. But a USB external battery pack compromises the weather seal. The Ion uses a locking rear cap with an O-ring that must be removed to access the USB port and other controls.
The Ion Speed Pro is a good value for $70 or less now on Amazon, but mostly as a daytime camera. The nighttime performance is mediocre, far inferior to the better GoPro models. I've used it on the handlebar and helmet. While it didn't come with a helmet mount it's easy to homebrew with some velcro straps. The cylindrical shape fits snugly into a cutout vent in my helmet. Much lower profile than any GoPro, or any helmet mount that uses a ball head. The ball head adjustment isn't necessary with the Ion with some helmet designs, and the 180 degree FOV compensates for minor aiming error.