When the larger putting grips became popular, two buddies I golf with tried them first. They were really putting well with the oversized putting grips so I decided to give them a test. Instead of running out and purchasing the larger grips, I build my existing tapered grip up with tennis wrap...used quite a bit and stayed with the large tapered style putting grip and I truly believe my putting improved!
With that said, I believe the oversized grips do work; however, I prefer the tapered oversize grip as opposed to the oversized grip that is the same diameter, full length...I just like the tapered feel. My buddies like the oversized, same diameter.
Hoping Geoff has some interesting input on oversized grips.