Without telling us exactly what the problem is, I wouldn't bother with any of those products. My mechanic and I tried quite a few of these products on my R56 and pretty much none of them worked long term. The fuel tank additives will help pass a smog check but if you already have codes coming up, they will be back. Italian tune-up and paint thinner both popular fixes didn't help long term. In the end, I spent more in time and $$ trying different fixes, I could've gotten one off the forums or salvage yard for less money and less frustration.
If your cat is clogged (check w/ borescope), you can send it into a company to have it professionally cleaned out. I believe they use mild acids and detergents to clear the matrix. You can also try to use a pressure washer w/ soft nozzle and blast it clean after soaking the cat in hot water and detergents. Be sure to fix whatever the issue was, mine was a leaky head gasket.
If the matrix is damaged, either physically or thermally, then you have very few options. Best bet would be to find one from a salvage yard or if your country allows it have a new replacement made.