Can I run the MainWP Add-On on my normal business live website?

Technically yes. However, it absolutely makes no sense! You should think twice if you really want to do that.

Maintainig your websites is a whole another task than presenting your business and/or portfolio on your website.

MainWP Dashboard should live in a dedicated, security and performance optimized single site install (regular WordPress way, non-Multisite!) and only be used for this one purpose. Then adding Toolbar Extras (base plugin) AND Toolbar Extras for MainWP (Add-On plugin) makes the perfect sense and will bring you the best results and time savings.