Like the B-Band AST and the K&K Pure Mini, the LR Baggs I-Beam is a soundboard pickup that adheres to the inside of your guitar, on the bridgeplate between your soundhole and bridge pins. In doing so, it produces a remarkably natural tone by picking up the vibrations of the soundboard (rather than the vibration of the strings, as with undersaddle pickups). The I-Beam is responsive enough that it will even pick up percussive effects and fingersqueak. Included with each I-Beam is a placement jig that makes the pickup totally self-installable (provided you have the hole for the endpin jack in place). I-Beams are shipped with extra adhesive strips on request in case you need to experiment with placement.
Please note that the pickup listed here is the passive version of the I-Beam. I usually strongly recommend going with the active version of this pickup, which has an onboard battery and volume control. However, if you already have an outboard preamp like the Baggs Gigpro or PADI, then you may be able to get away with the passive I-Beam.
The Baggs I-Beam pickup is available in two versions, one for regular steel-string guitar and one for classical guitar. They are essentially identical, but the classical version has a little arch cut into the middle of the pickup so it can straddle the center fan brace.
As a fingerpicker who wants to avoid batteries in my guitar, I've generally used the Baggs LB6 to much satisfaction. However, I have an old Guild that is my "strummer" guitar and I didn't think the LB6 would be a good fit for that when performing. I wanted a soundboard transducer that was passive, not boxy sounding, and would work with my Baggs preamps. It's hard to find the iBeam passive but Shoreline has it and I ordered one. It installed easily with no glue (!) and no other modification besides the endpin jack. I had been warned that it's a quiet pickup but I didn't find that it needed all that much gain to produce a good volume. Run into my Fishman Loudbox Mini with the volume between 1 and 2 o'clock, I only had to set the gain between 12 and 1 to get it up to power (for strumming, fingerpicking might benefit from more gain). There was no excess bass, no harshness in the high-end, and best of all, no feedback.
I haven't had a chance to gig with it yet, but I imagine that it will only benefit further from the detailed EQ and notch filter available on my Baggs Para DI. Perhaps it's just a good match for this particular guitar but I would sincerely recommend anyone considering a K&K to give the passive iBeam a try. I think it has an exceptionally natural tone for a SBT and doesn't seem to suffer from some of the issues common with soundboard transducers.