I've had both the AA powered models and the Li-Ion system. I recommend the Li-Ion over the AA. For me at least, I got longer run-times, and easier battery maintenance. I am currently using the 400L on my handlebars and a 140 tail light, both Li-Ion powered. In the two years I've had them, I have had zero issues. Dinotte's customer service is also first class.

I have never used the helmet mount, so I cannot comment to that. I do run a Princeton Tec EOS-bike on my helmet...highly recommend.

I have recently purchased a 18650 flashlight called the "blaze" from Shining beam. It is an awesome flashlight and so far has proven very good at being a bicycle headlight. it is really nice not having any cords to fuss with and batteries are plentiful. I keep an extra cell in my bag but so far I have not had to use it. Now if I can just find a version with a red LED to rival the 140, I would be set.