I bought a CO4 at MARS for $50, figuring it might a funny "effect" mike...but DAMN ! When I tried it out on my acoustic guitar, it sounded DAMN GOOD ! It is not nearly as tinney as most cheap dynamics (like the SM57) and has better low end than most.
The upper midrange is a little boosted, but it doesn't have any tinniness at all. The highs are very smooth, but don't extend extremely high, catching the "sparkle" like my earthworks mikes, but it is still a very good, smooth sound. The sparkle is something you don't really miss unless you hear it in an A/B comparison.
The biggest drawback is that like many dynamics, they have low output, so I have the gain cranked to 66 dB on my preamp. You need a high gain, low-noise preamp for soft sources like fingerstyle acoustic guitar.
I went back today and bought two more ! Great little mike, and built like a tank !