I haven't had the need for either one so far (knocking on wood). I don't use a great variety of threads, but I've been able to adjust the tension so far without a gauge. I know that a lot of people feel the Towa gauge is a necessity. Fewer seem to be using the gauge for the top tension. Even with the gauges, there is no magic setting that will always work. I understand that with the Towa you can tell pretty quickly if your bobbin is poorly wound, but I've been able to discover that just by looking at it. I wind my own bobbins, and the bobbin winder I got with my Innova usually does a great job of it. I would say that if you're currently struggling with setting tension, the gauges might help (especially the Towa) but if you aren't having a problem, why spend the money?