C8 is a form factor/size. The XinTD is a bit bigger than the older C8s I have. The reflector used in the flashlight can influence perceived brightness. A shallow reflector will spread the beam over a much wider area (flood) and won't be particularly useful for cycling. A deep reflector will result in a narrower beam (throw) and hence you get more light in a smaller area and it will light up the further away. You obviously don't want a laser and you don't want a standard light bulb :-) There are other factors that can influence beam shape and intensity as well.

The XinTD has a brighter LED and better shape beam for cycling. The only way to compare beams a priori. Photos or measurement with special setup are the best way to compare.

For higher power flashlights, you'll need higher power batteries to drive the led hard enough and for long run time, which is why I recommended the 3400 or 3500 mAh batteries. I always use protected batteries but there are plenty of people who use unprotected in a single battery flashlight. Using unprotected batteries in a poorly made flashlight can result in the flashlight driving the voltage down far enough to damage the battery.