I think that the collector design going straight back is a better design compared to the sideways collector and flange that bolts to the stock location cat section. The reason is the less bends the better for exhaust gases which leads to faster velocity given the right diameter piping is used for the application.
However, like some people on here have pointed out, if this header is used with the straight back collector then the cat section either has to be made up or get the header and cat section together from Moore Performance. On the other hand, getting the whole combo would still be nice because these two pieces of the exhaust will be worth it because of the craftsmanship that goes into each header and cat section.
If I remember reading right, any catback will be able to bolt up like a 2.25 or 2.5" and then a 3" if so desired with an adapter.
If I build the engine I am thinking then I would definitely like to buy one of these headers and most likely the cat section as well. It won't be for higher end power just low and mid so it would be perfect