[EDIT 8/29/22] This compressor is NOT suited for bass guitar. After more use I noticed there is a loss of bass frequencies noticeably reducing the amplitude of strings 4 & 5 (E & low B). This was not apparent at low volume testing at home. I wasn't able to notice until full volume play at band rehearsal.[end main EDIT. Some sentences following were edited or removed to reflect this conclusion.]I am exceptionally surprised by this budget compressor pedal!The paint and screen printing are both nicely done. The color is like a metallic red wine with clean, clear, white screen printing with no misspelled inscriptions. The knobs do not wobble and have firm resistance to rotation, except for the sustain knob which is slightly easier to rotate than the other two on my unit. The button has a definitive click when engaging/disengaging. Input & output jack retaining nuts are both tight and secure. The active LED is a bright red. I did not disassemble to look inside.The unit appears to be true bypass, as described, since it will bypass even without power connected and there is no discernable change in tone while bypassed. Of course, there is no battery option, and the pedal did not include a 9Vdc power supply.This pedal is a fixed ratio (12:1 perhaps?), fixed threshold, fixed release compressor. The Sustain knob is an input gain to push your input signal above the fixed threshold. The Level knob is an output attenuator only. This means that the Level knob can only reduce the output to compensate for the gain added by the Sustain knob. The Attack knob appears to go from unknown minimum attack time to infinity. In other words, the compression is not instantaneous with the knob at minimum and turning the knob to maximum appears to prevent compression altogether.An interesting note is that this unit can create an overdriven distortion when the Sustain and Attack knobs are both set to maximum regardless of the Level knob setting.I am testing this pedal with a 5-string bass with active humbucker pickups. The bass has a very hot output from the start. So, even with the Sustain knob at minimum the threshold is exceeded, and compression is occurring when the bass guitar’s volume knob is at max. Unfortunately, this pedal has a reduction in output when set to not compress (Sustain @min, Level @max, Attack @max). Therefore, when trying to set for mild to no compression the Sustain knob must be at about 9 o’clock for unity output, which increases the compression amount. My bass has very low self-noise and I did not notice any noise from the pedal besides distortion when overloading the input as described above.It will level out notes on mild setting and give distinctive squashed sound when pushed hard. I found the Attack needed to be set around 2 o’clock to accommodate the low B string. You may be able to set a little lower for 4-string bass and even lower for guitar. As expected, there is some loss of higher frequency definition especially when the Attack is set too low.I can CONFIRM the low cut that T. Nicholson demonstrated with his screen captures of SPAN. This behavior is probably beneficial for guitar but is terrible for bass.Getting a transparent reduction is not possible with this pedal. I believe this is due to high compression ratio. When the signal is compressed, you will notice the effect. This could be a pro or a con depending on your preference.As positive as my experience was with this pedal, I don’t think I will keep it for bass. I’m wanting a more transparent compressor that I can leave on all the time. I have decided to keep the pedal to use with electric guitar.