But it requires a long cage, which isn't a good idea with 20" wheels. While riding in the woods, I got a twig stuck in the derailleur cage, which is why I'll be swapping it for a short cage — and is fine for a 7s cassette anyway, and makes me wonder why the mfg chose a long cage.
52/34 + 11-28 = 1,83m - 7,14m = 390%
I've been using a double crankset + derailleur for years on a Brompton successfully. I don't mind the close/overlapping gears as long as I have the right gears for hills and flat. Besides, I rarely switch to the small ring — but am glad it's there when needed. I do touring, not performance cycling :-)