1991 C4 Muffler Question

I'd like to get my dad something for his car for Christmas this year and was thinking about one of the pipes that replaces one of the mufflers on his 1991 C4. I've seen a couple (Tweeks and Performance Products) but am wondering if anyone has used one before or heard of any results. I don't want to spend more than $350 or so. I'm not necessarily looking for much in increased performance because the car is more than he can handle anyway, just something that changes it some for him. Thanks in advance...Brent