I used to use them. Went to no finger inserts, liked it. Used no inserts for 7 or so years. I'm not back to inserts on my strike ball, my spare ball has no inserts. I find that I can get more on the ball because it feels easier to hang on to the ball when I go for more axis tilt. The thumb, I always used to get pre-formed ovals, but my last ball was no insert / raw ball in the thumb....love it.
So, insert, no insert? Only matters what's comfy for you. Someone I know uses 1 insert in the fingers, 1 without, both straight up finger tip drills.