I'm not sure if it breaks in. When the Sheath was my daily driver for the better part of 2019, I thought it had a great grip. But after a month of using the Apple Silicone Case, I now have a hard time handling the Sheath, and it feels like a bar of soap. (It doesn't help that my hands are dry because I'm constantly washing them throughout the day.) The only thing I dislike about my Sheath is that every element of the bottom is too sharp for me: 1. Where the rough texture meets the smooth material isn't applied correctly, so there's a sharp edge there and 2. The cut outs for the speaker and lightning cable are all sharp. I've tried sanding them down, but it's still too sharp, and I can't hold my phone for too long unless I adjust how I hold it. I've resorted back to my forest green Apple Leather Case. I'm going to force myself to stick with this case and have it be my daily driver from now until eternity.
(Meanwhile, I have another tab open on my browser, looking at the Speck Presidio Grip.)