I now use vise pro oval inserts. There is a difference in feel but not major in my opinion. I order one size smaller and then use a bevel sander and 220 grit paper to customize to my thumb. Much faster than customizing a slug to oval.
No, the thumb inserts will not wear out, just like the thumb slug.
CC
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Those that can do. Those that can't complain. Pimpin ain't easy, but it's mandatory.
Most things we like, we don't need. Most things we need, we don't like. Don't confuse your likes with your needs.