I've bought it mostly for use with one of my passive basses which has two single passive pickups. I wanted to reduce the noise from singles, and to shape a good signal for every situation. And this preamp makes it perfect with a ground lift option. I also often use it with my active basses too, when I'm not sure about the line signal on the stage, and it works perfect in these cases. M-81 was my long time wishlist favorit, since I'd been using their MXR m-80 for a long time. But I don't need an overdrive section and need a smaller pedal. That was another reason for m-81 version. Also I like the way it works with frequencies and overall output of my basses. The equalizer is quite useful and clear and the Color button gives you much punch. The only con to mention is that it doesn't work with fantom energy from mixing desk, like m-80 does. But it has so many attractive moments that I don't care. I use it with power supply. To make the long story short, this is a preamp that solves every question with my bass signal and I've been dreaming about it for a long time, so I would recommend it for other players.