Does what it says, load box that you plug in instead of speaker and then sends signal over digital out. I use it with DAW and impulse responses - Ownhammer free one based on Mesa cab and Redwire free one based on Marshall cab. Redwire ones are better, at least in free segment. Still I have to buy ownhammer but for free stuff Redwire is better for me.
I use this on my Mesa Boggie Express 5:25 combo and it rules. It wipes the floor woth any digital modeling stuff(including Line6 Helix, Headrush as they cannot replicate the dynamics and especially sustain that comes over with true tube amp). Cleans are good, can break a little but that is due to a nature of the beast - there is no speaker, just Impulse response that emulates it. Distortion is great, especially on bridge pickup as neck is little muddy(more than amp with speaker). Could be that some other IR can help with this but could be the nature of my amp.
There is no hum, no noise in the sound coming out on Digital out. Build quality is top notch, its like a tank. Digital out I keep at max 12 o'clock and there is plenty of output there if you need more.
I give 4 on features as it is little pricey for "just a load box", if it would have attenuation in it(reducing load and allowing some sound to speaker) then I would be happier but that is just me complicating.
I can play the crancked tube amp at 22h (thats 10PM) or later in total silence with my headphones... Awesome...
