I don't know that the company's even still going - certainly when i've bought 'Rhinox' diffusers online when they've turned up they've just been generic unbranded diffusers - exactly the same as what you'd get if you bought The Green Machine's 'Jap Style' ones. So I think Rhinox has just become a generic tern for a plain glass diffuser (like hoover, or biro). Certainly can't find a website for Rhinox.
In my experience it's luck of the draw with any of the 'budget' diffusers, Rhinox included.
To guarantee a good 'mist' you may have to pay for it. ADA, Cal Aqua and Fish Vet are reliable.
Or you could get lucky. My Rhinox 1000 produces the best mist I've seen from any diffuser, ADA included. I'm super-careful when cleaning it, as I'm a clumsy so-and-so...
That's not to say if you get a Rhinox, you're guaranteed the same results. My Rhinox 2000 produced bubbles from around 10% of the ceramic plate. My Rhinox 5000 around 30%.
As I say, luck of the draw.
My top tip would be to concentrate more on water movement to get the CO2 microbubbles shifted around the water column. This would be more beneficial than relying on the production of really fine CO2 bubbles.
That and keeping the ceramic plate clean with regular maintenance i.e. weekly bleaching. I hear Tilex is great too but am not sure if it's available in the UK.