I just purchased a Holeshot Jet kit for my 2001 B600s, It comes with the timing advancer
IMHO, the kit came with an advancer, so that says the kit was designed to work its best with it.
I've read Ivan's reports that they are a waste of time and money with
his 1200 kit on a dyno - the test bike lost half a horsepower. Dale says they make more difference in throttle response than in actual horsepower numbers though he claims they add power with
his kits. Throttle response is something the dyno is not as likely to reveal.
It's ~5-10 minute job to swap the trigger. Not too difficult to try it both ways and see for yourself which way works best.