Hi George,
I put a set of the Igaging scales on my Taig mill and they have worked fairly well for several years (4-5 maybe?).
I did have a problem with one of them a few years back - it started acting squirley, like you describe - jumping around seemingly randomly. I traced that to the read head not staying seated against the scale. I ended up making some shims to fit inside that helped hold the read head in place. It works quite well now. As it turns out, a few weeks after I'd fixed the problem, when I was cleaning up my swarf piles, I found a 2-3" spring that I'm quite sure is supposed to fit where I placed my shim that should hold the read head firmly in place. Somehow, the spring slipped out the back of the read head and caused that problem. Interestingly, I have never replaced the shim with the spring, at least not yet. I meant to do it, but it works, and I just haven't gotten around to it and its been years.
The only other issues I've seen with them is when the batteries get low. Then it also starts to act weird till you replace the batteries. I'm sure you've checked that too? Seems unlikely to be the problem with the new one you received.
Kim