Bromptons used to be great bikes, when they were still using common standards of fitment, so owners could easily customize or upgrade them with off the shelf parts. But like all these things the greed seeps in, they start making them so you need to buy THEIR replacement parts as nothing else will fit. Quality is way down too, both in terms of materials and workmanship, the finishing is dreadful and they are over priced for what they are.
But get a decent used one from around 2012 or earlier and you're looking at a completely different bike, wonderful to ride, easy to maintain and upgrade, lovely little finishes all over the frame.

Sad, but this is how it always goes when brands become popular, they move away from building a brand reputation, to simply milking the existing brand reputation.
You can't go wrong with an old Dahon for the money.