OK, where to start. IF you want the lightest version possible go with the Merc and buy the Ti bits from Brompton. I have a set of them. If you want a basic Merc but you want the rear triangle, I have one of those with a Brompton SA hub too.

What doesn’t show up exactly correct is that the Merc weighs more than a Brompton even with the Merc’s lighter frame because it has more accessories on it. It has a kickstand too that isn’t exactly lightweight. However said kickstand allows you to actually use the rear rack instead of folding it under the bike to act as a kickstand. The Merc also has a dynamo and a light too.

The front derailleur mount on my Merc is a clamp on and works fine. Don’t forget that the Merc also comes with the luggage carrier bracket and bag. An expensive upgrade on the Brompton.

As you have noticed the 6spd doesn’t gain you too much with respect to gearing range. I wouldn’t go with a Schlump Mtn. drive up front. I’d gear the front shorter and go with a speed drive or high speed Schlumpf drive. It makes more sense.

As for reach my Merc is more comfy than my Brompton was. Don’t forget you can slide the seat back in its mount too to extend your reach if necessary. I am not a small guy and I can get comfy on either bike. FYI I may be selling my Merc6. Not because I don’t love it (as I do) but I am looking at building one from scratch with a frame I will be getting from Merc. Mine has the amazingly upgraded brakes too.

One other major (for me) plus the Merc has over the B is I like the twist-grip shifter vs. the thumb ones on the B. Much more intuitive. One thing that is nice that the Merc has is the little clip to keep the rear from falling under the bike when you pick it up. This is a nice touch too. You could of course add it to a B and if I owned one I’d definitely do it.