Marshall "Edward the Compressor" ED-1: I reviewed this pedal several years ago, and in that review I said it cut off all the low end and had a big drop in output level. I also noted that another user said they had no such problems. So now I have finally gotten around to buying a second one, to give it another chance.
First, the new one works fine, so the one I reviewed before must have been defective. There is some loss of lows, but no worse than any other typical guitar comp. The highs are bright and crisp, and overall that's how I'd describe the tone of this pedal. It's a VCA-based comp, and it has the clear, hard, quick quality often found with that type. There is no drop in output level, and in fact it is capable of a significant amount of boost. It features an "emphasis" knob, which allows more of either the highs or the lows to pass through uncompressed. The range that is less compressed will be a bit louder than the other. This feature would be very useful in principle, but is quite subtle in reality.
The noise level is fairly low when the sustain knob is at a low-to-moderate setting. It's capable of some extreme squashing and sustain, but it does get noisy in that range. Just past 12:00 on the sustain knob, it is possible to get a high-enough ratio for peak limiting, without too much noise, and it does a pretty decent job of catching moderately-big peaks.
The construction is quite rugged. It runs on standard Boss-type 9V DC. The footswitch is not "true bypass", but the bypass is clean. The bypass of the first one I reviewed was pretty bad, and I have seen other negative opinions of the Marshall bypass, but this one in my hands now seems to have no tone loss. Overall, now that I know they don't all have the problems I experienced the first time, I can say this pedal is fairly decent quality and a good value for the price--as long as you can deal with the loss of a bit of low end, which would not even be so much an issue for 4-string EADG bassists.
Update! Andreas at stinkfoot.se says it is easy to cure the loss of low end by replacing two capacitors. Swap a 0.22 uF into the cap position marked C4, and a 0.47 uF into position C8.
Price in USD: $30-$60 used, no longer available new.