The new ones look more polished, and the hardware that controls the folding process seems more sophisticated. No idea about the sound--I haven't played one of the new ones.

Mine is set up for nylon strings, which was a key accommodation for allowing the banjo to fold without having to remove the strings and, indeed, without having to do more than minor retuning when you restored the folded instrument to playing condition. I don't know if the new ones can handle metal strings, which I suspect would be a necessity if you were going to play it with other instruments.

Another thing that certainly has changed and that's the price. If I'm reading the website correctly, the new ones cost about 5 times as much as I paid for mine. but of course withinflation, the dollar is probably worth about a fifth of what it was worth in the 1970s.