I have a Marshall DSL1CR 1W tube amp combo and it gets too loud for my apartment. By adding this JHS Little Black Amp box to the FX Loop, I am able to use it as master volume, so that I can use clean channel volume at correct spot for sweet breakup point. This thing saved me from having to sell my tube amp, so its a 5-star device for me.
The device is somewhat expensive on what it actually is, and you can find instructions to make your own with 20€ of parts. But the price comes from it being built in the US instead of China.