> Maybe he meant nobody else on the planet offers this unit except him.
> Is anyone familiar with any of the models listed.
I just picked one of the model numbers you listed and Googled it using "rhb-90atc". Close to the top on the results list was a thread from a Beesource member who was having problems. A bit below that was this Alibaba page listing about half a dozen Chinese wholesale vendors offering this exact model number refractometer:
I have no doubt that item is sold at retail in many different stores/sites, they just change the model number to make it more difficult to identify.
When vendors cannot describe their products accurately, run away!
Update: This vendor appears to offer the model numbers referenced above:
That page does nothing to inspire confidence that there is a reliable vendor there, in my opinion.