I had a Philosophers Tone awhile back, I sold it fairly quickly. If I recall it REALLY squashes the signal even on the lowest settings. It will definitely give you sustain though, almost infinite even clean. In the process it kinda makes all guitars sound the same. That much squash doesnt allow much personality to come through either ("dynamics")...but depending on technical prowess and rig that could be a benefit I imagine. Not disimilar to a really nice handwired amp compared to a cheap money maker, when a kid plugs into the nice one for the first time they says "wow, I can hear all my mistakes so clearly now".
I have an Electro Harmonix BlackFinger I use fairly often. It has 2 12ax7's (and is an EH) so its footprint is huge. The tubes give it a good boost tone though too, which is how I use it; tad compression and post gain. It has a seperate setting for "squash" heavy compression--I prefer my vintage DynaComp for that stuff though. Yeah Bobby was a big compression user after '74 I believe...its really nice for certain things, not really single note leads though. Its a big part of "studio" sounding stuff too, polishes everything up.