Everyone seems to love them and if the bolts aren't too rusty it's not hard at all to install yourself. Popular brands are Fabspeed, Circuit Werks, Top speed, NHP. There's lots of threads with pics, installs and video clips to help out.
Circuit Werks here as well. I ended up just cutting the old hardware out.
FWIW, I quickly realized that the rattle was not just the secondaries, but the primary cats on the headers as well, so I replaced them shortly after. If I were to do it all over again, I would replace everything at once. I have OBX catless headers with Circuit Werks bypass pipes and mufflers. Nice sound and fairly inexpensive.