The PDI-06 is one of the most bare-bone but functional units you'll find for absorbing an amp load, with a thru-output to run an incremental percentage of the absorbed load to the speaker.
What this means is that you can crank the volume of your amp, utilizing all the watts in, for example, a tube head or combo and getting that nice cranked tube-amp sound but at a lower volume. What's also possible is to completely absorb the load which would otherwise go to the speaker, giving you almost absolute silence.
Combining this with a DI box designed for guitar (Palmer PDI-09) you can send a Line level speaker simulated signal to your mixer or audio interface while having near silence in your room or studio. A very usefull tool for silent recording sessions!
The unit is built like a tank, just like all the other Palmer gear, and is meant to last you years and years. It's completely passive too, so no hassle with power adapters is needed!