I just finished installing Pro Soft Inserts in my 3-4-5 irons, then regripped them. With the grips off I did a vibration test on one club with the insert installed, one without. Big difference in the amount of vibration that travels up the shaft to the butt of the shaft.
I could barely notice any vibration in the club with the Pro Soft.

The only reason I will not do all my irons is I went to midsize grips on the irons I installed the Pro Softs in. I want to play a couple of rounds to see if I like the bigger grips. Then I will do the rest of my irons.

For anyone with arthritis or joint pain I would highly recommend that you put the Pro Soft Inserts into your irons.