Are they any good?

The one I saw had a cack connection and only worked when waggled!
You'd think the rep would check his samples worked first wouldnt you!!!

Hmmm not sounding too good so far then, pity as they seem really good value on CRC.

I have On-One's LUU light which is basically the same thing, except for cosmetics. Very happy with it; build-quality is ok, emitted light is plenty for GlenTress (with helmet light too) + the Pentlands (fine on it's own, on med. setting) – at the time, the LUU 4-cell was £75 cheaper than the Nuke-Proof, it might be worth checking On-Ones / PlanetX's site.
A previous related thread here…, which makes it sound a little weak at first, but honestly the power is fine – latest Singletrack Mag also has it on test – while it doesn't 'win', there aren't any real negative comments.