I've run them both... well sorta lol - I've the SBP one and a buddy has the Spooky and I can tell ya this, the Spooky one is LOUD! There's also the problem with the Spooky one that w/o a head pipe there's no real easy way to adjust it to fit your bike if it hits the pedal crank. Expansion chambers also need some length of head pipe for maximum performance... how much this effects it I'm not really sure because although my engine and his are identical, his is stock other than the pipe *shrug* The Spooky one is easier to mount, it's just a "bolt n'go"
if it fits... whereas the SBP one is a true full-length exhaust system that requires a little customization (trimming pipe length, routing) - but it's nice that you
can customize it...
Both of them do provide some performance gain, but given the problems with the Spooky one (may not fit, no headpipe, crazy loud, no rear support) I'd vote SBP - but you may like loud and it might fit perfect on yer bike - your call, ANY expansion system is better than the stock can