Cygolite Hotshot 50 has crappy side illumination, isn't water resistant, and really in this day and age, it's kinda big and heavy.
The Cygolite Hotshot Micro has really good side illumination, pretty water tight, last all night easily, can be used in day time riding effectively, and has some good group riding modes. Whats also great is that it's fairly small and light. Also if you consider ebay as a source, which I do, it can be had for less than $25. Also if you like to clip it to your saddle bag, or belt, or whatever, you can contact Cygolite and request a clip. they'll send you one for free. Why they don't include it into the light is beyond me.