If your worried about the finish, dont use a holster, and dont use the gun.
Both leather and kydex will mark a guns finish over time, just in different ways. Kydex usually only marks the finish at a couple of distinct points, where the gun contacts the holster. Leather tends to wear the finish more overall, leaving the entire finish looking worn, as well as wearing more at some contact points, as it contacts a lot more of the guns metal surfaces. This wear only gets worse with age, as the leather picks up more abrasive crud and diirt, which tends to embed itself into the leather and work on the guns finish. You dont have this issue with kydex. Kydex holsters also are very easy to clean. A quick rinse in the sink and dry with a paper towel and your good to go.
The biggest issue with leather is moisture and rust, something that is really a non issue with kydex. The kydex holsters will also long out live the leather holsters. I used to go through two, and sometimes three good quality leather holsters (the last set were Galco Royal Guards) in a year. One Blade Tech IWB lasted 10 years of daily use before it was retired. I still have it, and its as functional now as the day I bought it, 20 some odd years ago.