yosh makes a kick ass pipe however if you can afford it go witht he full pipe. slip on will add a tad of power and it sounds very nice, the full system sounds close to the same and adds a lil more power the just a slip on. either way i woould do it!
My Yosh RS3 is bloody loud but sooooooo sweet and lurrrvly. I can't take the bike to work any more as it is too loud for my return journey at 0300. Still I love it but it's pissing down raining outside and I haven't started my bike for more than five days now. Can,t wait till I hear the rumble of that exhaust again.
you can tune a couple to a few hp if you do a fuel mod like PC2 or jetting. It does benefit as it's more of a straight through rather than a pressurized can like the stock silencer. So it does have it's good attributes of doing a can by itself. By doing a good "tuned" header with the can though, you're looking between 8 to 11hp gained. I'm talking real hp though.
So a can's not a waste necessarily, but a full system is no doubt going to have its fuller function.