ItsJustMe, by "the 40 lumen" were you referring to the Serfas Shield? If it's 40 LM, how many lumens would you estimate the Cygolite Hotshot to be? Or, alternatively, how many watts does the Sofas Shield have? (the Hotshot has 2w) (You video is very helpful btw)
The con (for me) of using a cree headlamp with red filter is that you have to carry an extra battery pack and mount it somewhere near the back (or maybe keep in a bag on the rear rack).
The Cygolite is hard to compare directly with the Serfas (or most other lights) because of how tight its beam is. Check out this video I did (sorry I didn't have the Serfas at that time)
http://youtu.be/L95eIXswCb0
See how almost all the light for the cygolite is in the center? Also look at the video posted above. If the observer is right behind you, it's probably about 75% as bright as the Serfas, but at 45 degrees to the side, it's probably half as bright or possibly a bit less. It's still pretty good to the side, but it's not as bright as some of the others.
Given that the Serfas has been dropped in price down to $39, and the Cygolite is $28, it's kind of a tough call. I really think the Serfas is definitely worth another $10, but they're both good.