I haven't seen the kits from SC in person but looking at the pictures its hard to tell the quality.
From the pictures it looks as if the kit was installed and picture taken right away, it does take a while for the leather to relax and all the wrinkles to come out; if you have a hand held steamer it helps the process along.
If you look at the head rest in the photos you can see puckers in the seam line. It could be from bad seam work, wrinkles, not being fitted correctly when installed... You never know. The seam flap on the inside should be pushed to one side or the other until you get the best fit.
I've seen hundreds of leather kits installed over the last year, here are some things I would ask Bill.
What is the quality of the leather, as in grade.
Get color samples, they never match exactly.
Stitching type.
Is it padded at all.
Do they have fabric reliefs sewn in.
Are the Velcro strips sewn into all the proper spots.
What parts are leather.
What's the warranty.
Who pays for shipping if you have a problem.
How long will it take to rectify it if you have an issue. As in a piece being defective.
Make sure he has it instock and will ship right away
That's enough I think..
Some other things to think about. Your seat buns have shrunk over time, all foam does. You can plump it back up with a hand held steam but this is temporary, it will loose form again. You can build it up with foam.
Either way you will end up with sags or puckers in places,adding or moving foam is the best way to fix it.
My luck with Bill has been 50/50, fortunately or unfortunately depending on how you look at it he has a few things for the Mark you just can't get anyplace else.
You do have other options for leather.
Hope this helps.
J