Rocketeer and Gary T, thanks for the help. I tried spraying the handle with Plastidip (four light coats a half hour apart) let dry for an hour, went in to shave and PRESTO! No slippage! Looks a little better too.
I love Harry’s, and I agree that the handles need some texture. I use friction tape myself. It got scary there for a bit because I shave my entire head, and a slipping grip can be…bloody.
I like the heft and balance of the Truman, not so much the slickness.My natural clumsiness and parsimony led me to look for a solution here, which the Plastidip suggestion provided,