The nicest thing about blender is that we can run multiple versions side by side. I still have 2.81 installed, I'm using 2.83.5 now with all my addons, but I'm going to install this 2.9 just to see how it works and have all of them on the same machine. If 2.9 works good and I can install all my usual and paid addons without any problems then I might use it in place of 2.83.5. They will probably release 2.9.1 in a few weeks anyway.