For me it was a game changer. I just could not get the "hang" of the bobbin drop method (pun intended).
I kept getting uneven tension, and wasn't real happy no matter what I tried, and after getting the gauge I discovered some of my bobbins (they came with my machine) didn't spin as freely in the case as they should, and the tension would fluctuate, while others were fine.
Now I test every time I change thread, and found I can set it around 180-200 and then adjust my top thread and I'm having so much less tension problems. I also bought a digital readout for my top tension, as I always get messed up with the "lefty loosie/righty tighty" thing. So now when I turn the top tension, I can see if I went looser or tighter, and by how much instead of guessing.
I'll add that I never had a problem with adjusting tension with my Bailey, but that is a domestic machine and worked the same as everything else I had. The HandiQuilter is like other industrials, you have way more room for adjusting, so you may give the knob a 1/2 and it doesn't make that big of a change.