I have two Bromptons and my wife also has one. They date from 2001, 2009 and 2013.
An advantage of the Brompton, which probably acts against the company's interest, is that it lasts well and is maintainable over a long period - i.e. the parts for 2024 models are mostly compatible with the old models.
I did replace my original 2 Bromptons when they introduced the longer wheel base model and the version with titanium parts, as these were worthwhile upgrades for me. Since then Brompton have introduced improvements over the years, but until recently nothing fundamentally different to the main frame and forks, so I added the improvements I considered worthwhile to our existing Bromptons.
Brompton have, however, recently added two completely different new models:
- the ultralight T-line with a titanium main frame. Despite the very high price I would have been interested, except for the fact it has several carbon fibre parts, including the front forks. As I have experienced several knocks on my folded Bromptons during transport in the 23 years I have owned this make of bike I consider carbon fibre as unsuitable for my kind of use. IMO steel and titanium resist scratches and side impacts better than carbon fibre, which can crack and then fail catastrophically later on.
- the 20 inch G-line model with fat tyres and 8-speed hub gears. Again, I would have been interested, but this model has aluminium forks, probably for ease of manufacture as this model is fairly heavy and the rest of the frame is steel. I don't trust aluminium forks on a folding bike for the same reasons as carbon fibre - on a Brompton the forks are on the outside of the folded package and I have sometimes had paint damage with scratches on the forks on my steel Brompton. With a scratched aluminium fork I would worry about metal fatigue leading to a catastrophic failure - not pleasant on a fork.