Guyatone ST2: Surprisingly nice. This is one of their "micro" pedals, about 2/3 the size of a regular Boss pedal, from their older product line in the stamped-metal "dome" housing. It has the ability to combine the compressed signal with the dry uncompressed signal for a more natural tone, and this works quite well. The compression is smooth, with minimal artifacts, and a nice clean tone. With the dry "direct" signal switched out the fully-compressed signal is a little bit dull and processed-sounding; but switching in the direct signal really opens it up and gives a big clear sound. Interestingly, the compression overall is sufficient even with the uncompressed signal mixed in.
The highs are bright and clear, but the lows are cut off a bit. I'd say much like the Keeley and the modded CS3, the lows are perfectly sufficient for a 4-string bass, noting that the lows sound "tight" rather than "fat". Also, I was able to get enough lows to even sound decent with a 5-string by replacing the .022uF input cap with a .22uF, with no penalty to the highs. The noise level is very low unless you crank the Sustain knob up past 12:00. In fact, this pedal is much quieter than the Barber Tone Press, which is designed on similar principles.
The down side of this pedal is the construction quality- it is very cheap and flimsy. Also, while Guyatone has advertised that their newer production pedals are "true bypass", there are a lot of the non-TBP ones out on the market, so there's no real way to know in advance what you're getting. The ones I've owned were not true bypass, but their bypass is OK; the bypassed output level is a little lower than unity gain. So all in all, I like this pedal fairly well; I like it much more with a simple mod to the input cap; and I'd like it better yet if it was re-housed in a sturdier case, with a better footswitch.
Compared to the BL2, the ST2 has a clearer, more natural sound, with fewer artifacts; the BL2 passes more lows with no modification, but has dull highs; the BL2 is better at limiting sharp transients, but the ST2 is better at evening out signal levels across the high and low strings. Compared to the Demeter, the ST2 is not as fat, but has a little better highs. It's most similar to the CS-3, but the CS-3 is more "obvious" while the ST2 is more "neutral" sounding.