I use 2 of these helmet mounted (an H600F Flood and an H600 Spot). I have used them for about 6 months and had no problems whatsoever. I have them both helmet mounted and it does tend to make the helmet a bit front heavy without having a battery pack at the back to balance the weight, the lights themselves weigh hardly anything (about 40 grams) it is just the 18650's that weigh it down. I would quite happily cave with just the flood lamp as this does everything I need, but I like having the spare lamp already mounted on my lid it is useful for large avens.
It makes it quite easy to find yourself in team photos because you do stick out like a bit of a sore thumb with a strange contraption mounted to your helmet. Just to be aware, if you are ordering from the UK, they do take a week or 2 to arrive as they get shipped from China.