I’ve actually seen a few in concert.they are HEAVY, like dead body heavy. Moving one was like trying to get a drunk buddy home. 3) because them being so heavy and hard to transport I think they were just at studios more back then. Id suspect that most didnt use them, or didnt know how to, and come 1980's they got tossed in the dumpster.
The last one was when I went to see Joe Bonamassa at a taping of Austin City Limits. He did an acoustic set to open, took a break, then came back out to do an electric set.
His keyboard player at the time was Derek Sherinian, and part of his rig was a Leslie cab. It was pretty big- you could NOT miss it. It was also unmistakably present when he used it because he had it rotating pretty rapidly.