I use the round Rohloff shifter, the rubber abrades quickly, some day I might upgrade to the wave version.
But in the meantime, I wanted better grip than the round one offered, especially in wet conditions. I am in USA, there is a product here called Shoe Goo, it is a viscous fluid in a metal tube. You can put it on a shoe sole that is worn to replace the rubber that has worn off. A few days after application it has fully hardened.
It shrinks as it hardens as a significant portion of it is volatile chemicals, sometimes I put on a second layer. I put my shoes or boots outside while waiting for the volatiles to evaporate.
Why am I talking about shoes? I put three beads of Shoo Goo (black) on my round shifter, and it has added greatly to my ability to grip it and also it abrades less than the original rubber, so it is extending the life of that. Applied two layers. The three beads of it give it a shape more like the triangular grip. Photo is from 2016, it is still holding up well.