flowmaster doesnt make an exhaust system for the car as far as i know? what are you planning? do you want to make a custom axelback section with a flowmaster muffler or are you looking to fab up a full exhaust?
either way, a muffler wont make power, just change the sound of the exhaust. if thats what youre looking for then its a good project.
Its a 1.5L motor. You wont get much sound out of it. Not really worth it IMO. I'd suggest to get a nice intake setup. I say this because according to other members, intakes on the crz seem to give the car a more throaty sound, while adding pretty decent gains w/o the ricy exhaust 'buzz buzz pop pop sound'. Ive yet to hear a good exhaust setup that I like for this car. Honda engineered the crz to have a nice stock exhaust note. And it sounds great for a stock 4 banger honda. I really like it.
I agree with what borcth said. Look into getting an intake, because not only will it change the sound, but you will also see gains in power in higher RPM's, as well as slightly increased fuel economy. If you would like to get an idea of the sound change, you can see the link to my post below. It has a video clip of WOT from inside the car on the highway.
you will see gains from an intake but there is only one out right now. I do think an intake would be more beneficial but an axelback is def not a bad idea if you want more exhaust sound. The fact that its a 1.5l makes no difference.
if you are looking to change the sound and you only replace the axelback section you will not get rasp or popping at all. there are still 2 cats and all other stock sound neutralizing elements are there. Its also pretty inexpensive to get a muffler and have a shop make you a pipe that bolts up in the stock location.