I'm tempted by the mono versions because most of what I originally owned was mono. A mono lp was $2.99 and stereo was $3.99 and that made a big difference to me. But the mono boxed set is a limited edition, isn't it? So it could be gone before you make up your mind.
I wonder if with the stereo versions, is the sound still split between the two speakers? They would have something like vocals in one speaker and instruments in the other. We listened to these records like we were deciphering ancient texts.
I have vinyl boxed sets from god knows when up on a shelf in my closet. They've probably melted by now.
