Does the VB-101 feature a power attenuator?

No, the VB-101 only includes a loadbox, so you can play with your amp in silence. The "Speaker Thru" output allows you to connect the VB-101 to a cabinet and get the normal sound of your amp (true bypass) without any reduction in volume.

This allows you to record your amp both with the VB-101 and, at the same time, via the classic method with actual cabinets and microphones.