Attenuator effective enough to push the amp a little, but totally useless for playing volume "apartment", as long as your amp is natively an effective master.
However, I used loadbox coupled to a speaker modeling (convolution), and there is a treat level. Note, however, energy is tranformée heat and discharged via a rather noisy fan when you really push the master amp.
In the end, effective loadbox which is the main that I am probably a bit expensive nevertheless use.