You buy Brompton for the fold, not the ride is how I best describe it to people who ask.
We have owned our Bromptons for five years but they rarely get used.
One of the reasons I bought the bikes was to take small day trips with the car and bikes. Throw them in the back of the car and go to places like Niagara Falls and Niagara-on-the-Lake (wine country) ride around and then drive home. They fit in the car nicely and the idea is better than the reality. The bikes worked but were not as comfortable as our full sized bikes, so I bought a roof rack and now use our Rivendells for this purpose.
We have yet to take them on any overseas flights because I don't own the hard shell case yet and don't want to take any chances with baggage handlers. My neighbour who owns Bromptons with her husband stopped travellng with the bikes because they were more hassle than it was worth for them. They just rent bikes in the cities they go to. They did offer to lend us their hard shell cases so I am going to take them up on this and try it. If I like it I will purchase cases for us.
I have never fallen in love with my Brompton as much as I want to. The bike is all about compromises, with small wheels, wacky gearing and limited choices for sensible upgrades that don't cost a fortune. Knowing what I do now, I probably wouldn't have bought them. If I didn't need the fold the Moulton would have been a better choice as it was a nicer riding bike. The best thing about the Brompton is the fold. It is the most elegant fold that is so quick, I don't think any other folder can beat this.
I have always wanted to sell both bikes but my wife likes having them around for guests and her occasional ride. I am looking forward to our experiment with the hard shell cases and hopefully the bikes will live up to their potential.