I'm not sure they are that different really; they represent a confused and frustrated (not to mention intentionally stoked) section of the political right in this country. To me the world feels angrier. I would say they are probably going to be represented more like UKIP in the 2015 election; tonnes of votes but barely any seats. Another 'jolt in the arm' to the Conservative Party, taking them further right. Traditionally the UKIP/Brexit vote sits at about 600k, similar to Greens, but i see Reform echoing UKIP under Farage at much bigger numbers.
what will they become after that? god knows. the Torture Party.