they're good, but they're supplementary lights, not main lights (imo). The mounting works brilliantly, fwiw. If you get a lighter colour (mine are the translucent white) you get a fair bit of light given off from the casing too, which can help with visibility somewhat.
I clip mine through the vents on my helmet, personally.
On the bike, I have one of these;
http://www.knog.com.au/Product.aspx?productId=160
supplemented with a steady light.
Pro-Bike Kit had a set of rear & front frog lights on offer last year for £10, that's when I got mine.