I bought a brand new white PG-380 from a local music store in the 90's. It cost a fortune at the time but I really dug it and it was my main guitar for years. As mentioned, it is a bit on the heavy side - although probably not more than a Les Paul. I've heard that the guitars were actually built by Ibanez, with Casio adding the electronics and putting their brand name on it. It was definitely a good quality instrument and sounded fine as a regular guitar.
Going midi-out to a synth, the tracking wasn't great, but the fact that it had internal sounds was awesome and put it in a class by itself and the internal sounds tracked great. I was really into tweaking synth sounds at the time and since they weren't editable on the guitar, I went out and bought a Casio VZ-10M synth module, which is the same synth engine as in the PG-380, to use as a "workstation". I would edit sounds in it, arrange them in the order I wanted, and load them onto a ram card which went into a slot on the back of the guitar. That worked out really well and gave me some nice custom sounds. I also bought a couple 3rd party sound cards that were available at the time.
Overall, it was a very cool and innovative instrument at the time. The fact that it has a built-in tuner was nice touch, although I was never much of a Floyd Rose fan. But I really enjoyed using the guitar for a number of years. I eventually got into the Roland guitar-synths - GR-50, GR-30, and currently a GR-33 and VG-99. I sold the PG-380 to a keyboardist friend of mine a few years ago, but he recently told me that he wasn't using it much and wants to sell it. Everything was working fine when I sold it, but when I played it recently it had developed some issues so is not in perfect shape. But worthwhile fixing up for someone who wants a really unique instrument. As I recall, Bob Weir of the Grateful Dead played one for a while and they were officially endorsed by jazz great Stanley Jordan at the time. I'm surprised that guitars with built-in synth sounds were not really developed after the Casio PG guitars - too bad.