I use a Brompton daily for commuting. I've been using the fixed longer seatpost for the last year or so. Even so seat is lower than ideal. But then it's a folding bike! My tailor would say I have a 32" leg.
I've also started riding a road bike for triathlons. (Middle aged crisis etc) And I'm getting pain in a knee joint. It seems to be worse after riding the Brompton.
Now I reckon I'm riding the Brompton faster that I was and the lower than ideal seat height is to blame. Frequent starts with limited gears presumably don't help. What does the forum think?
Obviously I should get the telescopic pillar. But concerned it's more complication. And greater stress on the frame.