They are great.
Older consoles and carts are getting expensive/difficult to find in good condition/potentially prone to failure, especially CD based systems as the optical lasers don't last forever.
Not everyone wants to spend a significant amount of time and money dealing with all of that.
I have had more fun with my SNES and NES Classics than I have with my Xbox One X.
Purists will of course prefer the original equipment... And that is perfectly fine as well.
--::{PC Gaming Master Race}::--