I just know that someone, somewhere (even if not here on AB) is going to compare the appearance of those two gentlemen together as akin to the old circus 'freak shows' and throw their hands up in horror about them being 'exhibited' as abnormal.
However (despite the inevitable claims that they're being 'used' for commercial purposes - i.e. to promote the Guinness Book of Records), I see nothing wrong with them freely agreeing to come to London and enjoying their 'fame'.
I just hope that the organisers of the event did more than just bring them together and actually considered the practical difficulties that they must both face (e.g. working out how you provide accommodation in London, with a suitable bed, for someone who is around 2½ metres tall).