I have one of the Ted's extensions. A 15 footer I think. I got it before the DiMarzio was available.
The cable is pretty good sounding, but is not completely colorless. It adds a warmth to the sound, so if that is to your liking, get one.
I recently ordered and received the DiMarzio Big Red extension from HeadRoom. It definately is more neutral sounding, a bit more detailed, and is a step up in my opinion. The high end is not quite as smooth as I would like--it has just a tinge of hardness in the high end. This is going to be noticeable probably only if you have a pretty good source/amp/headphone setup.
In the end, I decided to return the DiMarzios and wait for the forthcoming (so we're told) Cardas extensions. Given what I heard recently at the Dallas HeadRoom show, it should be worth the wait!