Well, I have a CP-16R as well, and before I had it rebuilt, I used a GSMO on a shoot and loved it. I used it because I was a film school at the time, and no-one knew how to use it because they had problems threading the magazine. So since no-one ever used it, it was in perfect condition, with a perfect lens. That was my first experience with it.
Then I bought mine over Ebay, and of course it didn't run like the seller said it did, so I started taking it around town, and finally it ended up at Optical Electrohouse. George fixed it, and now I'm super happy.
Back to you questions. The GSMO is very light, the AC manual says with film battery, and lens it is 12 pounds. That is 5 less pounds than a CP-16R in the same configuration. It is much smaller than a CP-16R, I would say that it is similar in size to an Arri SR2. Also it takes the same batteries, chargers, AC adapter, lenses, and viewfinders as the CP-16R. So if you have the a nice lens setup already for your CP-16R, nikon's, ultra primes, etc. That would be great.
There are two bummers, the first is that the camera does not have the video assist port that the CP-16R has. So there are two ways round that, AZSpectrum offers a hard mounted B/W video assist which permanantly mounts to the camera. I didn't like that idea so much, so I got a Mazilview MAT video assist that clamps to the viewfinder. I thought that was a better way to go, so I could use it on both cameras.
The second bummer is that my speed control does not do 29.96 or 23.96. I think that is rather nit-picky, and I don't imagine ever needing to do those speeds, but that could be a deal breaker for some people.
The electronics are the fatal flaw with the GSMO, but George has worked around that beautifully in this one instance. So if anything electrically goes wrong from this point, it can be repaired.
Steve
