I've just got two of the 10w ones for my shed.
One lights up 15' x 20' really brightly, I've hooked it on the post about 6'6'' up so I can still reach the on/off switch.
It does just cut out without much warning, the red light come on on the side beforehand but you have to be in a position to see it which is unlikely. I'm pleased with them so far but only just got them.