This is The One
I went looking for a new pickup after I got tired of the quack I was getting with a piezo saddle pickup on my 1970s Gurian Jumbo Rosewood. The I-Beam had just been released. What persuaded me was a testimonial from a session player who used to place five Shure 57 mics in various locations to get just the sound he wanted. After playing with the I-Beam for a few minutes, he put all his mics away.
It's that good. I have them in the Gurian and two Taylors, a 355 12-string and a GS Mini (too many bad reviews of the Taylor ES clip-in magnetic pickup). The Taylors have the later model with the soundhole volume control, which is an awesome feature. I plan to upgrade the Gurian to volume control as soon as the trust fund kicks in ;-).
I've also installed two or three in friends' guitars, notably a couple of Martins that were cherished by their owners. If you're decently handy and work carefully, it's really pretty straightforward.
What makes this pickup so great is that no one would guess that your acoustic guitar is plug-and-play ready to look at it. No cutaway or control panel or battery box on the outside. That, and the utterly natural acoustic sound that comes out of the speakers.
I even did hot-and-cold tests with recording, playing through a Baggs Para-Acoustic DI vs acoustic with a Rode NT-1 large-diaphragm condenser. I liked the Baggs pickup better.
The GS Mini in particular draws comments nearly every time I take it to Open Mic. It's a decent-sounding small box unamplified, but it holds its own with any acoustic-electric when plugged in.
Be sure to unplug between playing sessions (plugging in turns on the pre-amp) and change the battery preventively every few string changes. I've been performing for nearly 50 years and a sound/recording guy for about 30 of those, and this is the best an acoustic guitar can sound through a system, bar none.