OK, so I picked one of these up, $80 shipped.
When I got home I picked up my Fulk, took a few swings like I normally would. Wasn't hitting a ball, just acting like it. Then I swung the jim_mer stick 10 times, same thing. Like I normally was hitting a ball. Then back to my Fulk. My 27oz Fulk now weighed around 12 oz haha. You should have heard the "whoosh" I was getting on my swings after swinging the jim_mer.
I feel like it's going to increase my bat speed. Also like said above, I can see it helping teach wrist snapping mechanics. I can't wait to get a live BP session where I can actually hit some balls with it.