I have a TOWA and I use it all the time. I don't always use the same weight thread on my longarm and once I got the TOWA set at the reading that worked, I just adjust the bobbin tension to that setting and I'm good to go, no matter what thread I've got in the bobbin. I find that when my bobbin tension is set to what the guage says it should be, I rarely have to touch the top tension.
I had my longarm for a few years before I got the TOWA and got along OK, but for me the TOWA is a real "nice to have" notion.