Best thing is to go to a meet and check out other exhausts so you can hear in person.
IMO, I love the M-performance exhaust and recommend it 100%. It looks and sounds great - very aggressive. Like you, I wanted an exhaust that wasn't overly loud and this fit the bill. Its tame when you want it to be and screams at WOT. It doesn't have much bass like some of the other exhausts, so it's not as loud in cabin (which I like), but you definitely will hear the difference vs stock. Look at the Eisenmann Sport and Akra exhausts as well, they are also great alternatives.
As for the V1, I usually put mine right below the rearview mirror - it's worked well for me.