I had a pair on the two rear shocks on a Polaris ATV. Worked fairly well at keeping the gritty, sandy muck off the shock rod so it wouldn't eat up the seals. IMO, I can't see what purpose they would really serve on a street bike though.

 

 

Designed for Dirt Riders and works much better than not having them so I am told. You must rebuild your shocks a lot. Street, they hold in the heat which is no where good. Oil is very thin when hot. I believe that just keeping your shafts clean as well as your threads. I rebuild many HD street shocks and at the (my) recommended 37K mi interval, and the owner keeps his shocks clean, the oil is black from heat but there is no real amount of external road debris in the shock. The same shock from a guy who never cleans his shocks, expect $18K mi or less before parts are worn out.

 

 

Used in combination with the seat vibrator, they keep the cooter juice from rusting the shocks.
Cross-thread points!