The blind hemmer machine makes the stitch you see on retail hems--you know when you pull one thread just right, it totally unravels the entire hem? It sews horizontally instead of vertically like your sewing machine, and only uses a top thread---there is no bobbin. The cover stitch on the inside looks luke a serging stitch, but outside are only tiny pin dots of thread. It does a professional job. Totally different from the blind stitch on a sewing machine. You can view a demonstration at
https://www.youtube.com/watch?v=UGuBwBGU9lE