I have been using Steemit More Info for a long time and greatly value some of the facilities. It was sad that that was no longer developed.
Do you need to uninstall Steemit More Info to add Steem Plus?
Is the side-by-side view optional / togglable? That feature gave me problems in Steemit More Info, especially with the images, but luckily you could turn it off there.
I just disabled the old extension. There have been issues with side by side, but I think Steem Plus fixes a lot of them.