I have only used this Rollbe a few times - quite some time ago as well, and it worked, I was having some difficulty measuring a neckline at the time.
I cannot remember just how long ago I bought this, I first saw this on the Sure-Fit Designs American site, and as of course I live here in the UK I then looked for this on the Sure-fit Designs UK site and bought it from there, also I had the option of having either imperial measurements or metric measurements and chose the metric. I tend to keep this in a drawer and had really forgotten about this, and I shouldn't have as I have been playing with Sure-fit Designs in the last year. Just one of those many things we buy and whilst they are useful, if not out and staring you in the face you forget about them.
I am about to venture into adapting a pattern for knit fabrics, and I know I want to adjust the neck, so I am now leaving this out where I can see it - perhaps it will make my life a tad easier.
To use this gadget as it rolls around from the start point, you just listen out for the click/sound it gives, and count them up in your head, it really is that simple, however the click/sound is very feint so you do not need music or the TV on whilst you are using this. The disc as it rolls around from the start to finish one rotation is 20cm