I think the $600 units are the Hualingan units, see a bunch of them on eBay. I've considered them as well as they initially seemed very similar in software interface initially. The Hualingan units are definitely cheaper than the Dynavin ($600 vs $850). Just be careful with those units. From my research, they seem to have quality issues. I think a few of the members on here as gone through some bad lots and are even considering (or have) switching them out for Dynavin units. The Dynavin seems to be more legitimate with local distributors worldwide, and they seem to continue to improve their product. IMO