I set mine up that way for the same reason, to use my shift arm with my rearsets.
My observations. It works fine but you will occasionally mis-shift. When you learn how to ride your bike, they way you shift gets ingrained into your brain and after awhile you dont think about it
When I got my bike back together with the upside down shifting, I hadn't ridden in 2 years. I had to think about it every time. It worked Ok. But every once in awhile, when I wasn't paying attention I would shift they way I learned how to and would accidentally downshift instead of up, with comic and sometimes scary consequences. I planned on going back to normal, but it would take some work.
So, it works OK. If you have another bike with normal shifting, I wouldn't recommend it. You don't want to have to think about which way to shift while you are riding. It should just be second nature. I'm not sure it has any advantages except you may be able to up shift slightly faster and it is sometimes easier to configure with rearsets.