I'll start this off with admitting that I actually like COSM. For those times when you can't crank an amp, it turns out to be a useful tool. Since I currently live in an apartment with two lovely ladies, I try to keep my noise to a minimum.
To do this, I mostly record guitar via headphones. I've used a few amp & effect simulators on the PC, which have been fine, but all seem to incur more of an performance hit than the CPU monitor would indicate.
Their modeling is reasonably good for most things, but for reverb it has not been anywhere near satisfying, not for spring anyway.
Since I use reverb as part of my tone quite frequently I've been hunting for that perfect silent solution. Even to the point of building a mechanical reverb circuit. Which worked FYI, but did not match the quality of a tube driven circuit.
I've owned the Marshall Reflector, Digitech Digiverb and Boss FDR-1. All of these were decent enough, but when it came to a convincing spring tone, the first two were no better than my computer. The third sounded quite good, but would introduce random reverb splashes even if there were no notes being played.
The Boss FRV-1 doesn't seem to have the same problem as it's predecessor. It runs quietly and as long as it's not being A/B'd with a real Fender amp, it's pretty convincing. The decay is nice and long and the tone control is very handy. It can be dark and muddy or so bright that your ears hurt.
When played in tandem with the Princeton Reverb, it's noticeably darker, and doesn't give quite the same quality of bright tone. In fact, running the pedal as a dry guitar, the top end of the guitar is somewhat attenuated, not quite tone suck, but more of an low pass filter. The advantage of this pedal would be running reverb on overly bright amps, or if you have to play in a venue with severe electromagnetic interference issues (such as my home) as there's no inductor coil to hum like a fridge when you want a big splashy verb.
In a mix it sits nicely and I'd be hard pressed to tell the difference between it and the real thing in a blind test, this might not be the case if I were the one playing the guitar as there is a marked difference between the two in terms of response to playing dynamics.
It's not a true substitute for the real thing, but it performs well for such a tiny package.
Sometimes a one trick pony is all you need.