If you are looking for a water bottle to fit on your Brompton, this fits perfectly & easily on the handlebar stem, and does not get in the way of the folding mechanism.

Yes, it's pricey, but it totally works, and is super easy to install (no tools required).

I love the super strong magnetic action which guides the bottle into place.

I used it on my Brompton P Line.

I was a bit worried about the water bottle size (I got the 590ml one), however if you want more water (which I did, as we did long rides on our Bromptons, in hot weather), take an extra 'insulated' larger bottle with you in your bag to top this bottle up throughout the day with nice cool drinking water & ice. Perfect!