I bought my joystick in October 2007.
The first wouldn't charge. Replaced under warranty.
When I went to use it after the summer break it died completely. Fixed under warranty.
At the end of that winter it started cutting out intermitently. I sent it back and was told there was an issue with the connections to the battery – I must have done this when I opened it up apparently. But I hadn't opened it up. I was told I would have to pay for the repair or they would do me a concession on a new model.
After arguing, they agreed to fix under warranty.
I've been using it through the winter (it is now out of the 2 year warranty by the way) and the intermittent fault is still there. Just cuts out every now and again. I do use it but certainly wouldn't trust it off roading with it.
So to cut a long story short, no they are not reliable. I don't expect to pay near on £150 for a bike light and have to pay for repairs or a concession (£70) on upgrading it within 2 years. I expect to be able to see where the hell I am going.