As both a guitar player and a bass player, there was a time when I started to be interested in compressors. For bass I quickly found the one that suited my needs, a Diamond Bass Compressor. But with guitar I struggled for a long time. Most pedals I tried were sucking out my guitar tone. Most of all, the highs were always cut off, and the overall tone lost its brightness and therefore a lot of its beauty.
That was until I found out the Xotic SP compressor, the first of a long series of Xotic pedals I bought. The feature that convinced me to give it a try is the Blend knob, that allows you to keep a natural attack and preserve your guitar's natural tone mixing the dry and wet signals together to your likings.
Another very interesting point is the size of this pedal. I have an overcrowded pedalboard (due mainly to a gigantic Octaswitch that I use to route mi signal), and I couldn't handle another regular sized effect.
The four internal dip switches are extremely effective. The first two control the attack and release time. Of course two knobs would give more room to set these two parameters exactly how each player wants them to be, but the four combinations you get from them sound very well, and I think anybody can easily find the balance they need. I personally keep them both on the Off position, to get a more natural compression (low attack and long release).
The other two dip switches are respectively a High Cut and a Low Cut filters. I keep the Low Cut in downward position when I play with my SG to avoid muddiness. With my Carvin TL60T, that has a SSS pickup combination, I keep it in the upward position. That gives me enough flexibility without making it too complicated.
I keep the SP on all the time on my clean sounds, and mostly off when my dirt pedals are engaged. I mainly use fuzzes, that are compressed enough and also don't love any other pedal in front of them, so there is really no need for extra compression. Nevertheless, for lightly overdriven sounds the SP make wonders, warming up the tone and making it somehow more fluid and mellow.
As for my cleans, now they are bright, have a tight but natural attack, a beautiful sustain and a more consistent feel. A great pedal, recommended to every player.