I bought the Skull Tailight. This is truly a stunningly bright light and it took several minutes for my eyes to clear the ghost flashes from inadvertently staring at it while playing around with the settings. It attaches very easily to my seat post which is a 31.8 mm (without tools of course), just stretch and catch the metal tab. I think one has to be careful on how far you manipulate the silicon band considering you have to remove it often enough for charging.
Charging it is really easy, it slides right into your laptop USB , and usually takes about 2 hours to be fully loaded. When you plug it into the USB it shows up with a solid red light and when fully charged it changes to green. There are several flashing modes and one solid, and I've found that this light lasts much longer when on a flashing mode. I am surprised that it doesn't last longer then 4-6 hours, but the recharge is simple and fast enough.
I knocked off one star because I think there could be improvement on battery life, but consider keeping it on flash mode for longer times between recharging. Other then that this is most definitely an excellent *be-seen* light and is a very versatile, easy application to your bike.