I’m being pushed to get one too and the information Eon sent me specifically said that there could be compatibility issues if I switched supplier. To me, the fact that they’ve mentioned it in the main letter rather than hidden in small print suggests it’s still quite likely to be an issue.
On the other hand, I guess that if it’s not compatible with your new supplier, you’re no worse off than you were before. It probably just acts as a dumb meter that has to be manually read.
There is also the security issue but I suspect that’s probably overhyped. Hard to tell for sure though.