1993 XO-1, early 1980s witcomb fixed gear, 1993 MB-1 singlespeed, a Surly 1x1 with pugsley front end, trek 520 converted to 650b, Coppi lugged road bike, Schwinn Crisscross townie
the racer kit has brake housing that is made of long strands of wire wrapped in kevlar (or something kevlar-esque). Basically it's shift housing wrapped in a non-expandable sleeve so it does not explode. Theoretically this leads to less energy loss when you apply the brakes, because the long parallel wire strands do not compress under load.
Jagwire's typical housing is fine for 90 percent of all applications. I would only splurge on the Racer kit if you have a good weather road bike and you are a colour matcher. It works well, in other words, but not that much better than the normal L3 Housing they sell.