I have never used or heard FF but I have used Prosound. It really brings the pinball experience to a whole new level. I have Prosound in all my machines now.
I think you will be addicted to the Awesome level of experience no matter which one you choose. My MM shakes the house when the castle is destroyed!
You will love it!

I’ve got the big 10 in my metallica. It certainly added a lot of bass. I remember thinking at the time the whole kit was a big upgrade... nowadays I’m not so sure. I’m much happier just adding a powered sub to my Aerosmith via the pinovators hookup. If you want to upgrade the audio I’d replace the backbox speakers and go powered sub, then you get best of both worlds.

https://pinside.com/pinball/forum/topic/flipper-fidelity-or-pinball-pro-1

I have never heard of “Prosound”

Appreciate your considering Pinball Pro, this is always a tough decision when you haven't heard for yourself. Please feel free to call and talk pinball anytime. We can discuss what you like specifically and determine which sound package will best fit your needs. Anything from 8-12", sub only, back box and external sub, volume control or not, lights no lights, etc

Greg M
Pinballpro.com