I added it to my Fusion, that and my TOWA guage were significant in helping me get past my tension issues. Some of the HQ machines come standard with it now.
I could never remember which way to turn the tension, and most often I would not turn it enough. Now I get the digital readout and know I'm going the correct way and how much. With use, I know about where I need to set it for different threads and that helps. You can't really go by anyone else's settings, you need to learn what it is on your machine, mine runs in the 500-700 range, and I've heard some people it reads in the 300-400 range.
I set my bobbins all around 180-200 and then adjust the top to balance.
For me, it was well worth the money and if I bought a new machine, I'd want that digital readout from the start.