The most easy upgrade for brompton besides hinge clamp should be the rear shock. Brompton stock suspension block has the reputation of "too soft", even with the "hard" block. With all these colourful choices of after market suspensions and all those stiffness modes to select, which one better suits your need? It all depends on your riding preference, how fast you want to go, how much is your weight and the general road condition of your rides. Oh, don't forget the weight of this component and the all important "BLING" factor. :)
Here are some test videos FYI. Do take into account the load (rider's weight) and road conditions.
A. Multi-S Premium Coppery Rear shock
Hard mode (PU inside)/Load:75KG/Road condition:flat, pebbles, hop
Soft mode (Spring only)/Load:75KG/Road condition:flat, pebbles, hop
B. Titanium Spring (<60g)
Hard mode (BOM inside)/Load:75KG/Road condition:flat, pebbles, hop
Soft mode (Spring inside)/Load:75KG/Road condition:flat, pebbles, hop
C. BIKEfun Rear Shock Colors (with
Bling factor bonus)
Soft mode 1 (Soft PU): on flat road with some jumps / Load : 60KG
Soft mode 2 (Soft PU): Test on climbings / Load : 60KG
D. Chubby Rear Shock from MiniMODs (Chubby mode for heavy Load >90KG)
Test video TBD
Not the end. To Be Continued .................................