This does work, except: put it on DRY leather. If you put it on damp leather the ink will bleed and smear all over the place. Putting it on dry leather will give you a nice, crisp, clean line.
Also, I use the acetate overhead transparency sheets to make the transfers. Being able to see through them makes it very easy to get very precise placement of the design on your leather. Then you can just wipe the remaining ink off and reuse it multiple times.
If its a clean line, its very easy to bury the ink in a swivel knife cut, and I use a pretty thin blade for any intricate carving I do. Beveling, backgrounding, etc. buries it further, and it also tends to fade as you work along, so by the time you're done you really can't see it at all.
Kate