My wife bought me one for Christmas. Will agree that it likes heavier leather over light. After working out a few bugs, I'm happy with it for stitching 10oz belts. Not so happy on lined 4-5 oz stuff. Top stitch will look ok but bottom leaves a lot to be desired. Ithough, have had good exerience with their customer service. Could not get bottom tension adjusted when I first got the machine.....bobbins jammed into the shuttle and it appeared they were too long......I thought possibly a bad batch of bobbins. I called..... they sent more out right away. That did not fix the problem.......bobbins still too tight in shuttle. Called them back and they sent a new bobbin shuttle out right away. Of course, by this time I had already ground and polished on the ends of the bobbins (approx .020") to get them to spin freely in the shuttle. Seems to work ok now. In hindsight, I think I would recommend spending a bit more on a powered machine. You will get a much more consistent stitch out of a powered machine. My biggest complaint on the Boss is lack of consistency in the stitch...specifically on the stitch lock. 10 stitches will be perfect and then a couple will pull the bobbin up too high. I'll probably sell mine before too long and upgrade to a Cowboy or similar.....
Reb