The SG20 was the very first module I got. It fitten onto the base of my palm IIIx and was slightly smaller than a packet of cigarettes. It was a GM module that had a midi in/out box that you could attach to it, although I never used this.
The quality of the sounds was excellent, and I always enjoyed using it, but as with all these things you get to a point where you say, actually it is too big / cumbersome / too many bits of kit to lug about, and that's what happened. In a way I wish I'd kept it, but I know I wouldn't use it at all.