The M1 consistently generates heaps of praise for its easy installation and great tone. I've installed a number of these as well as using them onstage, and I can report that the buzz is totally justified—this pickup rocks. It's a magnetic soundhole pickup, similar to the Fishman Rare Earth, but its tone is remarkably acoustic for a magnetic. The tone is no doubt helped by its individually-adjustable pole pieces, which let you adjust your string-to-string balance. And what really sets this pickup apart is the flexibility of its installation: You can hardwire it internally or do a temporary installation with equal ease. The pickup is packaged with internal wiring and a long external cable, all of which meet the pickup with 1/8" miniplugs, so you don't have to solder a thing. This means that you can hard-wire it into one guitar, and then when you want to switch instruments, just unplug the connector and move it easily to another guitar using the external cable.
The standard M1 listed here is a passive pickup, and is best paired with an external preamp like the Para Acoustic DI, but the M1 Active adds an internal battery and preamp, eliminating the need for external preamps, all for only $30 more. The Active version also features an onboard volume control, but does not include the external cable. It's also worth checking out the new Baggs M80, which is an update to both the M1 and M1 Active.