I use them occasionally. They arent the absolute best for burning compared to fresh lithiums, but they will keep a steady power going to it longer than alkalines or lithiums. When my lithium batteries stop giving green light from my laser, they still register as having little over half power left, which is bad since they cost a lot. Nimh batteries will keep giving about the same power until they are almost dead.
It really just comes down to if you want it really bright for a short period of time, or pretty bright for a longer period of time.
Well I use NiMHs AAAs in all my lasers.The lower voltage is probably kinder on my direct driven red laser.The lavadrive BR is just fine with them since the lavadrive just supplies the same amount of current for a long time if the voltage is anywhere between 2.2V - 5.5V (as I recall...).The only laser they suck in is the DX30 because it goes dim pretty fast because of the linear driver....but the laser sucks anyway so they might be good in a good quality CNI. Besides they are the only rechargeable option for 2xAAA lasers unless you want to use a lithium and a spacer.And I just don't like the idea of having a huge chunk of metal whose sole purpose is to conduct.