Congrats on the bag! I've always used Wilson's TLC to pre-treat/waterproof Koobas. Wilsons also makes a leather lotion/conditioner that works well too. I know some others use the Appleguard or Lovin' My Bags, but I haven't, so can't speak of those products.
Congratulations !! I got my first kooba last week also a Jacinda. I think it's great! We don't have such a great range of care products in the UK, think I might try the Mulberry spray unless anyone can suggest anything better.