The Retro-Sonic is the closest thing I've found to my original CE-1, for sure. In fact, after sending Tim Larwood, the man behind Retro-Sonic, a short clip of my CE-1, we agreed that it sounded a little brighter than his copy, and as d1dsj mentioned above, he sent me a very helpful photograph showing the component I could bypass to get closer to the sound of my CE-1. As you can hear in my demo, in isolation (cork sniffing mode) there are some subtle differences, with the CE-1 sounding slightly more open to my ears. But in context with a full band (battle conditions mode) the subtle differences disappear, and what becomes more important is that you are not lugging around the substantially chunky CE-1, with its connected power cable, inherent impedance mismatch problems and general quirkiness. The Retro-Sonic does an excellent job of being a pedal board friendly version of a CE-1, including the brilliant vibrato mode and its 'poor man's fast Leslie' offering, conveniently foot switchable with the chorus mode. Highly recommended if that's the chorus sound you're after.
Cheers...................................... wahwah