Have to say, it seemed like a weird one at first - especially with how the gain/leveling works, but I have now been able to compare it with an original CE-1 and is very close.
First of all: it comes with the internal switch set to "true bypass" so the preamp is completely disabled when you disable the effect pedal. You need to this to "buffered" for the pedal to behave exactly like the original CE-1 and keep the preamp active at all times. This should help with tackling level differences as well when engaging/disengaging the effect.
I have compared to the original with guitar + synths. On the original, the vibrato effect can be turned up to be a bit more extreme, but this could just be because off high tolerance in component/control values. The chorus sounds very similar! The preamp sounds very similar between both when moderately pushed. The original, when turned up all the way, actually broke up the sound in a not so pleasant way (with some nasty low frequency distortion). The Behringer didn't do this, it sounded more compressed over the full frequency spectrum. So while the preamp didn't react exactly the same, actually the Behringer preamp seemed a bit more useable over the whole level range. Maybe this particular CE-1 needed servicing as I believe it was still 100% original.
For synths and other line-level sources, both the Behringer and original are not ideal because even at "low" sensitivity, the preamp will distort pretty quickly. So if you want to maintain a clean signal, without any distortion, the output level will be pretty low.
When connected to my interface, I actually got quite a bit of noise with the original CE-1 (probably a ground loop). This was not an issue with the Behringer.