OK, so I've been using the Philosopher's Tone for about three days now, and I feel like posting some initial thoughts. This is one of those pedals that requires a lot of experimentation with different settings and basses etc. to understand it well, so this is not a "proper" review and I will not be posting a proper review for at least a few more days. These are just my initial impressions:
It's essentially a clean optical limiter with an extremely high ratio. When you raise the threshold it acts more transparently, when you lower the threshold it becomes an ultra-squasher. The envelope is the most unusual or hard-to explain aspect of the effect. When your signal crosses the threshold, it gets dropped below unity, and then the signal swells back up above unity, raising the volume of your note as it trails off, effectively increasing sustain. The more sustain you demand, the higher the noise floor, and the more bizarrely squashed your notes will sound for the first half-second. So it is capable of extreme sustain as advertised, but the penalties to your sound may not be worth it, depending on your tastes. At more "natural" sounding settings there is a small increase in sustain; but even at the more natural (high threshold) settings the attack of the envelope of the effect is kind of weird. Rubbery and squooshy. Sometimes I think I love it, sometimes I think I hate it. There is no loss of highs or lows, and the overall tone quality is quite nice. The noise level is fairly low, unless you set it for a lot of sustain. There is a blend knob for combining the compressed and uncompressed signal; this helps fix the weird attack shape to a certain extent. There is a "grit" knob which adds a layer of distortion to the signal. I mostly don't like the buzzy sound it makes, except for the lowest settings, where it is a passable low-gain overdrive. If you use the grit and the blend at the same time, phase cancellation occurs, which totally robs the low end and the guts of the tone. So IMO really the grit is only useful at its lowest setting and unblended. There is a treble rolloff knob, and it doesn't do a whole lot in the bass guitar frequency realm. It's not "bad", it's just not very useful. The pedal runs on 12-18V DC, and comes with a 15V wall wart.
As a peak limiter it is excellent, as long as you don't mind the odd attack shape; also bearing in mind that if you let a loud/strong note ring freely, the sustained portion may raise up higher than the initial note level, not being limited.
All in all this is an excellent and very versatile pedal. It was sent to me as a loaner to review, but I am probably going to buy it to keep. It's easy to abuse the settings and get very bad results, and finding the good settings is not super easy, so this pedal won't be for everyone. Also the attack shape may put some people off. But if you like the attack, and you work with it enough to find the right settings, this pedal has a lot to offer. I didn't like it at first, but now I really dig it a lot.
Again, this was just a first shot of my thoughts after only three days of use. I will almost certainly change my mind about some aspects of it, perhaps several times over some days, before I think it's ready to be a real review.