I got the medium kit out of this lot
http://furnitureclinic.co.uk/Leather_Colourant_Kit.php#pricesThe colour goes a very long way and i did 2 a full rear bench and 4 door cards.It covered everything really well.
I had to buy an extra bottle of the leather cleaner/solvent for removing the old dye but all the other stuff lasted really well.
The bottles of propellant for the airbrush however suck.They freeze up after a minute or 2 and it gets really tedious,so in the end i made up an adapter for the airbrush and hooked it up to the compressor at 40psi and it was 300% better!
It is a fairly time consuming job,but take your time,dont rush,mask off all areas you dont want dyeing as the dye stains anything.
You get 3 choices of finish and i went for satin as i didnt want a glossy unnatural look to the leather.
If you run into any problems gimme a shout but i found if i rang them with a query they were very helpful.