This one is a performance tool however. I hate the way pickups make an acoustic guitar sound. Usually pretty artificial and crappy.
This box takes the vibrations from the pickup and, on the fly, translates them into what your acoustic would have sounded like if it were mic'd up in an isolated studio setting. Fishman have taken specific guitars into their studio and recorded them, matching the recordings to the pickup vibrations. That's how it knows what the mic'd sound would be.
There are some guitar make specific mic'd sound models in this pedal, for like the classic Gibsons and Martins and others in various body sizes: jumbo, dreadnought, parlour, 12 sting, etc. And you can choose different mics too.
Anyway, you dial in the modelled sound, with maybe 50% pickup sound and 50% model sound and it makes your guitar sound so much more natural, nuanced and dynamic. If only I was a better player...
The box has got a tuner, eq, compressor, effects loop and other stuff built in, so it's pretty useful. But most of all it takes the edge off that crappy pickup sound and helps me relax because the guitar actually sounds right live on a PA.
If your specific guitar isn't modelled there are lots of guitars that are close enough, but if you want perfection you can even send Fishman yours in the mail and for $200 they will even record you a model specific to your actual guitar. With different mics.
Anyway I have been loading this one up today since I plan to do an open mic this week, work permitting.
EDIT: I saw a rig rundown video recently where Jason Isbell said he actually uses one of these too and says he can't tell the model from a real guitar. I knew it sounded good to my untrained ears, but from someone so dialled in this is a reassuring endorsement.