Jipe,
Good, detailed info, thank you. Regarding:
For the 3 years stem replacement, its a recommendation as part of the maintenance plan in the Birdy user manual, its not mandatory (the user manual says "Visual check, replace after a crash or 10.000 km or
3 years (whichever comes first)"). Its a usual recommendation for the safety of aluminum parts due to the well known aluminum material fatigue sensitivity. You find the same recommendation from Brompton for the aluminum handlebar and hinge clamps also made of aluminum.
I'm aware of the increased fatigue sensitivity of aluminum versus steel, which is why, bike parts made in aluminum are typically sufficiently strong and stiff to have good fatigue life. My 30 year old cannondale frame, the very long seatpost on my Dahon, seatposts on other bikes, handlebars, caliper and v-brakes, etc, all of these aluminum parts are designed for very long life without structural failure. Same for the telescoping aluminum stems on my Dahons. To specify a 3 year consumer life on something like a bicycle, not warranty against defects, but expected service life, is ridiculous, in my opinion. This appears to me, either, the part is underdesigned, or this is a shot-across-the-bow by R&M to obviate any lawsuit in the event of a failure. I'm hardly a flag-waver for Dahon, I've experienced poor customer service from them, but at least they don't require replacement of their stems every 3 years.