What works well as a plug and play replacement of the stock OEM catalytic converter for the M30 535ia engine?

Obviously, another factory OEM unit would work, but is quite expensive.

How about an aftermarket unit that would splice into the stock OEM stainless pipes, which could be cut to remove the old OEM cat.?

For example, how are Magnaflow or other stainless steel units, in terms of noise and durability?