This is a pretty high quality attenuator. The cool features on it include the impedence selector, which will let you optimize the sound for your amp situation (and prevent an amp blowout). There is an amp in, which takes the signal from the amp, and two cabinet outs, which will take the signal to the cabinet after the Leash provides its volume reduction. There is also a switch for bypassing the unit, and a fan to release some of the energy. The unit's only real delicate control is the large volume knob on the front, which is simply a level adjustor. The concept behind this type of device is interesting to me. The idea is that the box will allow you to achieve the desired tone on your amplifier, and then adjust the volume so that you maintain the character and tone that you desire without having to pierce your eardrums. This is often hard to do, as most good tube amps don't sound their best until they are really cranked to the max. For small clubs and rehearsal rooms, this can be a problem, as a good tone might mean that the guitar is all you hear.
There have been a few attenuators made over the last decade or so, and they've all had various degrees of effectiveness. Because people either didn't know how to use them or weren't aware of the impedence levels appropriate for their setup, they often blew out speakers on a regular basis. This model is one of the better ones that I've heard. I'm actually quite impressed with it. I've tried it with a Fender Twin, and I've been amazed at how well the raw power of the roaring twin was brought down to a reasonable level for practice. I've tried it briefly on a Marshall and was similarly impressed, the roar of the stack was tamed for practice-friendly volumes. This is a good thing for people who play in smaller confined spaces, or have roommates. This way, the tone can remain the way you want it, at any volume. Great for musicians who play small rooms or have volume limits.