Is it not the purpose of the experimental category of aircraft to be a proof of concept before continuing to full certification?
? ...
It depends upon whose Experimental category you are talking about. Vans, and many others, in the US has sold thousands of kits into the American Experimental category.
The HX50 is not going to be in an 'Experimental' category in the UK or EASA-land, it will be an amateur built aircraft operated on a Permit to Fly.