Very. That's why Lollar isn't cranking them out like sausages. Essentially the bent metal starts under the coil, and then after the bend, goes over the strings. That makes the portion over top of the strings the opposite polarity to the top of the polepieces themselves. In other words, the top of the polepieces in the coil might be north, and their bottom south. Since the part of the pickup that gets folded carries the polarity from the bottom, the string sits between north and south. If it wiggles side to side, it's no different than a regular pickup. But when it wiggles up and down (which a string normally does anyway) it is sensed by the polepieces AND the folded portion. That results in a greater sensitivity. More is discussed here: Horseshoe pickups: what do they do that's "different"?I'd never heard of these! Now I really want to play one. I wonder how hard it would be to build one of those pickups?