I actually bought a second folding pedal from a fellow Brompton rider, who prefers SPD's like you. I have several folding pedals, but they all fold outwards of the pedal. The Brompton design is smarter in that it folds *inwards* of the pedal, saving a massive amount of space in comparison (although care is required to avoid scraping the rear triangle at some crank angles when folded).

Here's the combination I use (yes, my chain needs oil :-)) which involves manually lifting the chain from small to big, which I find ok, as I only need the small ring on steep, say 1 in 8, & steeper.

If you search recent threads you'll find EvilV has posted some info' on front mech's.