I used it last night, with an 872 on the helmet. Bloody awesome.
Cars kept stopping down the lanes, which I thought was very polite, until I saw them shielding their eyes. Whoops.
Had to turn it right down when not riding at the front though as I was casting massive shadows for the rider in front.
Not run it for very long, but it does seem pretty robust and is amazing for the money.
http://www.roughrideguide.co.uk/off-road-mtb-light-pack.html