I have done some research since the original post. The box is simply a plastic project box with (2) 1/4" jacks and a volume pot. I was skeptical from the beginning since it works in the effects loop, and therefore only controls preamp output to the power section. My amp already has Pre & Post controls.
I did find that some users found it useful with Fender blues Jr. type amps, which apparently have touchy volume controls (poor taper).
I think I will stick to headphones with my Boss GT-5 for now. If only Bugera would come out with a V5 head or V5 combo with 10" or 12" speaker. I just don't care for the lack of bass response of small speakers.