It sounds like a bosal exhaust. As for sounding like Greddy, not that I can recollect b/c the greddy gets more shrill when wide open throttle is applied. This was seems to stay more consistant. Wish I could figure out how to get my Laptop to record a sound byte of it at idle, running at 3k and wot. I am not too sure if I like mine at this point. Still getting used to it.
i just purchased the mazdaspeed muffler the other day. i think it sounds great. i haven't heard the greddy exhaust, but the mazdaspeed one is deep and throaty. i recommend it.