Hey Murray, good to see you!
Hmmm, interesting stuff. Seems unsettlingly cheap, but kinda tempting. DRO is an upgrade I seriously want. I'm always wary of cheap gear, but as you say it's much the same as digital (optical) calipers. Mounting a set of calipers on your slides is a time honored way of adding a digital (or dial) readout- so in a sense it doesn't really have to be expensive....