Code P0430 and Engine Stumbles When Accelerating

[X5Cat]

So, I suckered and joined one of those "ask a professional" websites ($5 for a 7 day trial). Here is what I got:

Bank 2 cat doesn't really do anything to need change. It's just there for emissions. I recommend do a tune up on your car, new plugs and fuel system flush and new air filter if needed. Please let me know if you need further assistance.

Forgive me if I'm a bit underwhelmed. Seems to me like Bank 2 cat does the same job as Bank 1 cat, except it's on the other side of the car/engine. It may just be there for emissions but if it is off it can complicate engine management, right?

I saw another answer on that site for the P0430 problem, where the BMW mechanic said pretty much without hesitation to just replace the Bank 2 cat, and implied that it wouldn't be an O2 sensor since there were no O2 codes triggered. Not so sure about that, either.