I have a Handiquilter Sweet Sixteen. I use a lot of different threads, including 100 wt. poly and 100 wt. silk, even some 12 wt. cotton, as well as a lot of 40 wt. Isacord and Glide. I have several different bobbin cases- one for very fine threads, one for the 40 wt. threads and one for the thick threads (12 wt.). Even so, I test my bobbin tension with every thread and adjust accordingly. I have never used a Towa gauge, though I've been tempted to buy one, but usually I'm happy with my tension if I test it by laying the bobbin case flat in my hand with the open side down, and lifting on the thread. If the tension is right, I can pull on the thread to raise the bobbin case up so it is standing in my hand, but it doesn't come out of my hand. In this position, if the thread pulls easily and smoothly from the case without changing the orientation of the case and without lifting it out of my hand then I'm usually good to go.
Once I've adjusted my bobbin case so that the tension test works as described above, then I fine tune it by adjusting the top tension. I do this every time I load a new bobbin, even if I haven't changed the type of thread. I also check the tension on a scrap sandwich whenever I start a new bobbin, or if I've been away from quilting for a day or two. Works well for me. I think that's also the test that Jamie Wallen uses.
I hope that makes sense.
Rob