Had the rear light on all my bikes. It is extremely bright even at long distances, it lasts a whole long time and is extremely durable.
Easy to unclip.
Had 4 of these on several different bikes. Great bright little light to be seen with (not bright enough to see with) but two of the front lights failed after exposure to rain which is poor i think - this is England - it's gonna rain....
The rear one has been fine but i couldn't recommend these unless you can guarantee you'll only ride in the dry.