I only had the LS50 and LS50 Meta. The Meta sounded better. Better clarity for sure. Maybe that was it, I do not remember all the particulars now. I do remember thinking that this was a nice upgrade.
My system was very revealing at that time so maybe that was a factor in me noticing the differences.
I was initially planning on getting the original Kef Ref 1 but the LS50 Meta and the KC62 sub seemed as good in my small room. The only speaker I liked more in the space was the Magnepan LRS+ with the KC62. The LS50 Meta was better with respect to clarity and detail but the wall of sound of the LRS+ was favored by me.