The black widows are a very new marker on the market and I have only seen one or two places sell them. Personally I think they look cheap and tacky, just another spyder clone. I am not even sure what company makes them. Because they are an unknown company then it may cause a problem if your marker goes wrong and you need help fixing it.
I would highly recommend getting something like a piranha or even a black drgun. They will be cheaper and more reliable.
Or if you have a little more money to spend then consider getting an Action Markers sentinel. This thing is really well built, slightly more innotive than all the spyder clones, and comes in some cool colours.
www.actionmarkers.com