I have a single wire cutter that I purchased from Soapies Supplies (don't think they still exist) about 15 year ago. Mine has a Handle and knobs to tighten the wire string to cut soap. That makes it easy to keep the tension on the wire tight. I wouldn't want that loose guitar string wire that is in the picture. Also, where I place the soap log is a flat wood piece longer than my log. That helps keep my soap log in place. The photo looks like the place for the log is too short for most logs. I would be concerned that it would be hard to keep it aligned for cutting.
I really like my cutter. I assumed that I would move up to the big boy cutters with multiple wires but never did. I really like the flexibility of changing the width of my bars as needed. That way a log that weighs less can still be cut with a comparable weight of other bars.
So, yes, I like this type of cutter but I think this one is missing some important points, the cutting handle being the biggest. I would continue looking or look for directions for making them.