so what is the difference?
What are you looking for???
http://yoyoexpert.com/product/duncan/hayabusa/
The SL version makes it bounce more. Hayabusa has rubber rims, SL has softer rubber rims, so it bounces more when you drop.
SL = Soft Landing.
Like rsmod said, it has softer rubber rims.
Yes it does bounce more, but if you use the regular version on a hard floor, it bounces pretty high on its own. So each version works just fine.
Hope that was at least a little helpful. ;D