Firstly, I just want to point out that the use of "world's first" really doesn't deserve the discussion it's had. Yes, it's overused, but merlin know what they're doing here (shame the same can't be said when it comes to the parks themselves)
Secondly, im going to contradict myself and discuss it. I personally hate the use of world's first when it such a pathetic, meaningless claim as this. "World's first coaster fully dedicated to virtual reality" comes to mind aswell. World's first used to mean something when it came to new rides at these parks. The world's first on air, oblivion, and even th13teen were groundbreaking. World's first Gruffalo themed ride? World's first coaster fully dedicated to VR? Who cares?
I do agree though, that the GP seem go for theses weak claims. It's a marketing strategy that obviously works for merlin. But in this case, would "world's only" not work better? It's not like other parks are desperately trying to create a second Gruffalo ride to beat Chessington's world first claim is it?
To be completely honest, I don't care. It's such a minor thing that I'll forgive it if the end project works out. If this is the worst thing about this ride I'll be very impressed.