Starting off with the foldable M500 cans, their lightweight aluminum construction and memory foam earpads make them pretty comfortable to wear, though the sharp edges on the metal could use some sanding down. In terms of sound performance, the cans didn't do so well with noise isolation at the busy venue; but even when we tested them in a quiet room, we couldn't feel the warmth in Alison Krauss and Diana Krall's voices. In KEF's defense, the demo units apparently didn't get much time to warm up before the event, so your mileage may vary with their 40mm neodymium drivers.
The aluminum M200 in-ears, on the other hand, impressed us a lot. Once we got the hang of fiddling with the flexible "Secure Arms" and sealing the silicone tips into our canals, the pair of dual-drivers did their job almost perfectly during our brief ears-on. Compared to the M500, the M200 buds have a more unique layout (as pictured above): in each bud, a 5.5mm neodymium mid-to-high-range driver goes right up to the end of the tip for better clarity, leaving the larger 10mm driver all the way back in the chamber for more oomph. The resulting sound was both clear and had the right amount of weight across the range. Given our short experience so far, we'd definitely pick the M200 over the M500 for the value and noise isolation at least.
In Hong Kong, a pair of M500 cans retail for HK$2,680 (about US$345), whereas a pair of M200 buds will cost you HK$1,680 (about US$220).