I have the LR Baggs tune-o-matic system in a guitar and think that it is great. I would imagine that installing one on an SG wouldn't be that hard, it should be easy to eliminate a volume or tone pot on the magnetic side. I don't have any experience with the Fishman system but I would imagine that they can't be that different.
I'm not opposed to the LR Baggs system either. I have one in my Variax 700 and it's an awesome bit of technology. I just want another piezo electric guitar like my Dean (best tone my ear has ever heard). If Line 6 made a modeling guitar with humbuckers it would be a done deal. i like the SG (although the neck isn't as nice as the one on my Variax). I'm also thinking maybe a Warmoth project if i can get the line 6 neck.
What really brought all this to light was when I took my Dean to a "luthier" just because I wanted it cleaned up better and gone over by a "pro". Figured i'd have new strings and a setup done (guitars over 10 years old) and when I got it back it was dead! Of course the guy said it was fine when it left his shop and it took me a couple of weeks of tracing everything to get it working again. I was lucky enough to find a wiring diagram on the Dean site, but there is little or no info on the PZ model. The tone on this guitar is like a little slice of heaven to me. It has an arena rock/80's hair metal sound (dimarzio humbuckers model # unknown) that is unbelievable to me.
I need to build something close that I know what it is so I can make sure it can be fixed if something goes wrong and while I'm at it get the neck I like. I haven't found anything I like better then the 10" radius line 6 neck. Between that and the heritage cherry SG look.. If I can pull this off it will be one kickass guitar.
It's not totally the same, but my tele has a Fishman VT Powerbridge. The previous owner also installed the powerchip as well. My only complaint is the fact that mine's an active pickup system, and when the battery starts to go, you experience a pretty noticeable drop in quality...not just tone, but sound altogether.
At the same time, I love being able to tame off some of the treble and mix the output between the powerbridge and the other pickups. For my tele, the volume pot for the fishman replaced the tone knob.