Just to add on to this - if you buy this unit in the UK I think it comes with a different regulator that cuts the power output dramatically. This is reflected in the diff in rated power output between the manufacturer site and the UK places that sell them. More info: Power differences in gas...
Not directly related to your original post would OP would welcome your input on this thread I just posted: Power differences in gas burners between US and EU/limited availability of high power gas burners in UK
So I bought one of these recently (ANVIL FORGE BURNER - ships with UK compatible propane adapter) - rated as 11.4kw (39,000 BTU/hr) on the website (yet seemingly 21kw in the URL slug)
And on the manufacturer's website, it's listed as 80,000 BTU/hr (Anvil Forge™ Burner | Forge Your Next Brew!)...