I’ve used the S2+ and other tube lights strapped to the helmet w/ 2 velcro straps, long enough to go between the helmet vents.
And a long lanyard looped into the helmet just in case. It’s been rock solid for me for a few years when I was still night riding
on my 170mm travel MTB (ie not on smooth fire access roads).

Without any sort of mounts, the key is using a helmet that has grooves near the center. Fortunately one of my helmets is perfectly suited
for a light so I use it as my dedicated night helmet.

Short of that, I think this is a great mount, with or without the gopro adapter (gopro adds more height to the light, might get knocked off
by branches):

For the handlebar light, this mount is rock solid down the chunkiest trails, I and many of my buddies use the same mount: