Shift pro has a bearing. It was the first to have one. We did the same conversion that mull does on my buddy's bike and it's nice. I found that their star definitely is a little nicer then a modded stocker.However with the stock shift star modded it tends to work better with a stiffer stock spring, the mull star works way better with the softer shift pro spring.
After hearing so many guys say stock springs work better with modded stars, I swapped my shift pro spring out for the stocker with my mull star. I went to the drag races just to get some holes or practice on my TT motor. Man, I was getting spanked by all kinds of shit missing shifts with the stock spring on the Mull star. Even neutral was a bitch to find I yanked the clutch cover and swapped the shift pro spring back on to it and god damn, my tranny was butter again.
So stock modded star, use the stock spring
Mull star, definitely a lighter spring.