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. -Wavshrdr
With all my steel framed bikes-one dating from the 1960's-I go with a simple approuch to improving when it comes to optional accessories. I either do without it, subsitute another brand that might even do the accessory in question far better, or live with it until it breaks. Like modern cars, bikes are becoming more and more cluttered with excessive junk.
On the gearing thing. When I first got it, I felt it was over geared, and planned to get a smaller front chainring, but now, I don't think it is, and as I got more confident in it, I realised I could stand up on the pedals and push hard on the 45inch bottom gear and get up almost anything I come up against. -EvilV
The old English 3 speeds, the Brompton, and now it's competitor and mimic the Merc, is based on a basic seemingly limited range of gears that in actual use, is far more adapted to most range of terrain that I encounter here in my rather hilly neighborhood. My chainrings are all in the mid-forties and the rear cogs are probably similar in diameter. I never seem to honk or whatever the performance orientated rides seem to do on hills. I don't want to damage my good business clothes. I simply gear down to the level I need to accomplish the task at hand without too much taxing my body or bike.
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. -Wavshrdr
The grip shifter is a nice touch for the performance person. But I find that the trigger shifter is more easy to replace, and to gently shift into another gear without grinding. I don't care to race my bike. As for the clip, I buy one when I get around to it. I prefer to let my bike quickly fold in since I take it on public transit alot. If I need to keep the rear end from dropping when I pick the bike up, I simply use a short bungee cord for right now.
For your purchase of either the Brompton or the Merc, let me sum up what is the most important part of the bike-that is you and your wife. That variable is the most forgotten and neglected part of the bike/rider "relationship." The only difference I can tell between the two bikes is the frame (steel-Brompton or aluminum-Merc) and all the fancy add ons offered at purchase. One of the things that Brompton offers is the retro fitting of most of it's accessories and even components like brakes. I go simple and see what I actually need as I go along with the "C." If there is a next time with another bike, I would know what I need and want and go from there. It is a growth thing with me. Confidence grows with knowledge of my needs vs. what the company wants to spoon feed my ego. Then I end up with what I want rather than going broke or trying to pass off the bike on another unsuspecting soul.