I just saw an interesting marketing e-mail for outrageously expensive, knurled, freely revolving thick barbells.
My thoughts; while watching a strongman contest, when the axle clean and press is announced, we pretty much know it is a SMOOTH, NONE REVOLVING implement. It is this way to keep the "spirit" of the old time strongman shit alive (Apollon etc), and to make it a CHALLENGE.
If you are trying to improve your grip, one would hope you would shun the knurling. This is on par with pounding your blobs with a ball peen hammer to make them easier to grab.
Grip people using knurled, revolving barbells or dumbbells is like a man squatting to pee. ;)
Something to think about before your wallet disintegrates to the lure of guerrilla marking.