I've got K&Ks in my Lowden, two Martins, and a Fylde mandolin. Alan Marshall fitted one, I fitted another, the third was fitted by Vintage Guitats in Norwich, and the mandolin pickup was fitted by John Le Voi.

All four sound excellent, but they go through a Source-Audio Programmable EQ and an Orchid Muting DI. Straight into a PA they have a tendency to sound bass-heavy and thuddy, but using the EQ and DI they're very good indeed. And no batteries in the instrument!