there are a few youtube vids that show sidewalk shoe repairing and sandal making done in Thailand or Pakistan etc. These guys use the machine day in, day out, and know how to use them. You don't see them making purses, jackets or saddles with it, though.
Tinkerer's Delight is a true statement. I have a knack with mine now, but I still wouldn't try to get a professional looking stitch on fine leather with it. I use mine to repair things like the doggie seat cover in my pickup, making small canvas articles and such. I even repaired a pair of my own sneakers with mine. The hardest part of using it is keeping the seam straight with one hand while turning the crank with the other. You could add a motorised pulley to it, but I ain't gonna bother.
So yeah, even though I have one, I'm still hand stitching my leather projects.