Pharrari

So yeah my friend said he would not install my header unless I had a muffler hooked up to it. So I was like I guess I'll have to wait to come up with the money to buy a good one. So he says his friend is selling some sort of greddy universal muffler. So, the question is what are the pros and cons getting a universal muffler versus a proper fitted muffler? And if it needs to be welded on, how do I take it off if I want a different muffler if I decide to go with the universal muffler?