Zig-zag can be very useful for a stretch stitch substitute. But in reality unless you want to bind off the edge (which zig-zag is not real great at but it is faster than heat sealing) The need for a real stretch stitch is minimal. The issue that I would look at is the power to go through a variety of fabrics. Two things to look at, how fine and how long the feed dogs are under the p[resser foot. Dollars to donuts the cheap machine has a short set of feed dogs and they are probly somewhat coarse. That means slippery fabrics like silnyl will bunch and clog and wrinkle and just generally drive you bonkers. The industrial machine probably has a much longer set of feed dogs. Two reasons for this. It is a beeter made machine suitable for a wide variety of fabrics including silk and such. Secondly, like a boat... the longer the boat the straighter it tracks... the longer the dogs the easier it is to sew a straight line.
The cheaper machine has a motor that will dfo household sewing. That means if you are doing several layers of taffata and two layers of webbing and who knows what else, you can kiss the cheaper motor good bye, or you can hand turn the drive wheel. The industrial machine will plow through anything.
Do the math... for my money.. the industrial machine wins hands down.