In search of a stomp box compressor, I narrowed it down to the Xotic SP Compressor and the Keeley Compressor Plus, both in the same price-range. I chose the latter, as it is supposed to be quieter (less self-noise), and all the controls are on the outside whereas the Xotic SP has various options on the inside in the form of dip switches.
I use it in combination with a Gibson SG (which comes with very hot pickups) and a Koch Jupiter 45C amp and I like what I hear.
PROS
It gives a nice round, full (attack) sound when solo-ing and finger picking. I like it less for strumming chords, although that is probably a personal thing...it does what it has to do as a compressor. And it has a nice sustain, even on low settings.
The tone knob is a very handy, nice and essential option. The fact that it is a true by-pass pedal is always good, too. It has a mixing-option to mix the original, non-compressed sound with the compressed sound. This, for me, is an essential option, as well.
I use it in subtle settings...it gets overwhelmingly compressed pretty easily. I suppose it is nice that this is possible, as well, but for me personally, I have no use for these extreme settings. This might be different when using a guitar with single coil pick-ups.
Oh, the toggle switch to set for use with humbucker or single coil is great, too.
CONS
I (have to) use it with a 9V battery as a power source. To change the battery, you have to unscrew the back of the pedal. I'd like it if changing batteries was a little easier.
On a side note:
I bought a power supply (PSU) from Thomann for this pedal. Using the pedal powered by this PSU, I get a pretty nasty, constant, high frequency beep-tone (that increases in volume the higher I turn up the sustain knob [and obviously also when I turn up the level knob]).
This high frequency tone disappears for the most part when turning down the tone knob on my guitar completely. As that is clearly not a workable solution, I tried out a 9V battery. Now the high frequency beep tone is no longer there, making me think that either the PSU is causing the problem, or my electricity net. (Using another Thomann-bought PSU turned down the volume of the high frequency tone, but did not make it disappear).
Just thought I'd mention it, should others experience the same thing and think it is due to a faulty compressor unit. (For the sake of completeness: I tried it with different guitars, on another electricity group, with different guitar cables, but only taking the pedal off of the electricity net by using a 9V battery, did the beep tone disappear).