After some earlier posts I have been asked about leather restoring a few times, so this time I thought it'd be as easy just to do a new post - save on emails. I used Liquid Leather Scuffmaster (copied the order details below). The colour match was very good (black leather) and the little white crease lines in the leather soon went - it's a wipe-on / wipe-off application. If you have bigger scuffs try applying with a tooth pick.
Sample before -

Here's what I did:
Cleaned with Zymol.
Wipe down with damp cloth (around the scratch only) and leave for 5 minutes
Wipe with cloth with Liquid Leather
Use tooth pick to pencil in the cracks
Wipe down after 1 minute
Wiped over once more with Liquid Leather
(proper instructions with the product)
After:

It says to dilute 10% with water but I've not bothered, just applied with a damp cloth.
Order details - for my black leather:
Your order from http://www.liquidleather.com has been recieved and is processing.
Product : Quantity : Price
Liquid Leather Scuffmaster 65ml Kit BMW, Z4, 2003, Black : 1 : £12.85
The Liquid Leather site is quite good, listing the different colours - you can mail them if your's is not on there. I did a small test on an out of sight part of the seat before I went for it. I now just keep the dye in with my cleaning kit and any time the seats start to look a little worn I give them a wipe, works well IMO
I haven't tried any other products but this seemed to work for me, for black leather.
Sample before -

Here's what I did:
Cleaned with Zymol.
Wipe down with damp cloth (around the scratch only) and leave for 5 minutes
Wipe with cloth with Liquid Leather
Use tooth pick to pencil in the cracks
Wipe down after 1 minute
Wiped over once more with Liquid Leather
(proper instructions with the product)
After:

It says to dilute 10% with water but I've not bothered, just applied with a damp cloth.
Order details - for my black leather:
Your order from http://www.liquidleather.com has been recieved and is processing.
Product : Quantity : Price
Liquid Leather Scuffmaster 65ml Kit BMW, Z4, 2003, Black : 1 : £12.85
The Liquid Leather site is quite good, listing the different colours - you can mail them if your's is not on there. I did a small test on an out of sight part of the seat before I went for it. I now just keep the dye in with my cleaning kit and any time the seats start to look a little worn I give them a wipe, works well IMO

I haven't tried any other products but this seemed to work for me, for black leather.