Originally Posted by
blakcloud
You still get the slick internal hub with the 6 speed, the only difference is that is the it has a wider range between gears than the the 3 speed. Also what you call the front derailleur is actually in the rear. On the IGH there are two cogs instead of the usual one, which gives you the six gears you may need. Your left hand shifter, shifts between these two cogs. Simple design that works.
As blakcloud says, no front deraileur, just two cogs in the back shifted by a simple derailuer controlled by the left hand and even with single speed Brompton or any of the other gearing options you would have a little device back there to take up chain slack when you fold the bike anyway. The right hand shifts the internal gear 3 speed hub.
I would go with the 3 speed if I was a flat lander or did not plan to travel - maybe even the 2 sp or 1 speed. But for any but the most gentle of hills I would go with the 6 speed.
Hopefully you can try before you buy. The 6 speed takes a little getting used to because double shifts are more common than with a conventional drive train. However, the learning curve is very short. When grade changes quickly you learn to omit a left hand shift and skip a gear. When a double shift is called for I do them simultaneously. Like driving a manual transmission car it may seem confusing at firs but quickly become intuitive. I really don't think you would regret going with the 6 speed and will be glad that you made the choice.
My only other thought is that if you don't need the quick compact fold of a Brompton there are a number of other folders that could fill the bill.