I use and love them (so I wouldn't grip the puppy too tightly, just tight enough).
Having a larger diameter grip helps avoid cramps, and in my opinion feels great!
On my WeeStrom, they helped with vibration, but that has never been a problem on the 1100.
I imagine they have a limited life, however my guess would be that it should be many years.
Mine have taken on the shape of my hands quite a bit and in the compressed areas have much less "give". This doesn't appear to make them any less comfortable, in fact may make them more so. There is no sign of the polymer breaking down, and mine have been in the sun for about 80,000 km (well, sort of).
A must have farkle for me.