Harley Benton PA-100 Power Attenuator

This thing can be used both as an attenuator and a loadbox. Other much more expensive options don't even allow you to connect cabinets with different Ohm. This one allows 4, 8 and 16Ohm. The speaker out is self explanatory... Just connect it to a cabinet. If you don't want to connect a cabinet, just use it as a dummy load. As soon as you connect it, even at full power, you'll get 3dB of reduction. Of course you can lower its volume until it is pratically inaudible. You also get a line out and respective volume control. The XLR output has a cabinet emulation. I honestly didn't test it as it's useless for my use case and usually this kind of emulation is bad anyway, so don't judge the product based on it. The included fan is really silent and only works if it has to. The construction is all metal, really solid and it has an industrial look to it. As for the sound, I used it with an 100W tube amp, connected to a cabinet. I tested both with the attenuator and without the attenuator and didn't notice much difference in sound, if any. If there is one, it's subtle and you can adjust it with the amp's eq easily. Overall it's excellent for the price.

I use this on my Marshall DSL20 + HB 212 Vertical cabinet to play mostly metal and hard rock.
I turn the Marhsall dials to 11, and this one sits around 1. I did not notice any tone mudding (or sucking) that could not be slightly adjusted in the Marshalls EQ.
I'm not a tone nerd and for my "play at home" and "dream of being in a band" skill level fits perfectly.
The fan does not make any noise at all.

Disclaimer:
I did not test the line outs, so cannot really comment on that.