My motor's never been run without the jag so I can't attest to any difference. But if it reduces vibrations, isn't it worth it just to save the lower end? People say to keep WOT riding to a minimum but I do it everywhere, all the time, at 38mph, my milage is garbage (80MPG) but I've never had an issue. Racing applications are vastly different than street/daily driver. Maybe the stock CDI is faster, I dont know, remember the jag CDI is tunable (and yes it has given me mild gains and even introduced ridiculous vibrations if I set it differently), but in racing when the motors are rebuilt frequently, reliability only needs to last the race. I've never blown a bearing, despite how frequently people say it happens, wrist pin, lower, crank, not a single one, even after ripping the motor apart and cutting... pretty much everything.
So, I'll have to say, from how few problems I have with the motor, I'd say the jag is worth it, in conjunction with other anti-vibe mods (balancing, lighter reciprocating weight, good mounting, etc.) you could have a motor running in 4-stroke reliability territory. Not to mention my exhaust barely gets hot enough to boil water after running for hours @ WOT (I know because I ran it non-stop until I ran out of the 2L of gas). is it the CDI? maybe, I don't really want to run a stock CDI but if it will put the argument to rest for good, I'll do stock CDI, and each of the 9 settings on the jag and post hill climb speed/time, top speed, temperature, and 0-60(kph) time. I don't really have a way to quantify vibrations and we all know after a while of having vibrations you get used to it or you go numb, either way will bias the next test.
I dont like bias, I prefer solid numbers because they're unquestionable (unless people say the numbers taken are biased, but... I hate misinformation and this'll be a good way to see if it'll be worth it on my next build anyway so, why not?)