Hi Barry
I have a spare 125X airbox and it looks the same as the one in the ebay ad (from memory) however without being able to compare them side by side, you would never know for sure. I would expect them to look similar but the 250 one would/should be larger overall? Certainly the inlet boot would be bigger.
If you want I could take some measurements or you could borrow my spare one?
Cheers
Craig