Michael–
I would recommend getting the both. You won’t be disappointed by either one.
Both kick it up a level and show you more.
Some would depend on what areas you are doing the most work with. The supernova is more versatile, but
I haven’t found anything that is as good as the Gemini for T spine. Way better than 2 lacrosse balls taped together.
On both of them you don’t know what your missing until you are exposed to something that is better than what you have. Both of these are an upgrade on options that came before it.