I have had my genuine Apple Cosmos Blue leather case on my iPhone 8 Plus, since launch day and it is holding up really good!
The leather is still scratch free and still feels really nice. At the beginning, it was quite slippery and smooth but now, it has a really good 'grippy' feel to it - kinda sticky (not literally!) like (I can hold it on my open fingers at 45 degrees and it won't slip off), like the leather naturally grips your fingers and hand.
I've tried using some other cases (when I get bored!) but I always come back to the Cosmos Blue!!!
Its formed a nice patina with most of the colouration happening around the edges.
I like it.