I would describe the sound as "quietly throaty".  The exhaust note is not particularly loud but it is not anywhere near as quiet as my 15 year old Honda.  

All tubular manifolds are noisier than a cast iron one.  Exhaust note is essentially the same with both.

I tend to use either the MG Metro/carb'd Cooper or SPi/MPi cast iron manifolds with aftermarket downpipes.  The Maniflow ones for the MG setup are tricky to get aligned right initially but are easy to live with after that, the MPi ones are much more modern with a simple bolted flange.

Doug, hows the noise with that setup?

Oddly enough, I also have a more or less standard 1275 with dual HS2s and an RC-40 dual box exhaust.  I was recently faced with the same decision as you.

After reading threads here and on other boards I came away with the understanding that the Freeflow was easier to fit while the LCB may be better on a more modified engine than mine.  I bought the Freeflow. 

The Freeflow was painless to install and connected directly to the RC-40 system without any problems.  I had been running the factory stamped 3-branch tubular extractor (-S).  After installing the Freeflow I did not notice any change in the way the car drives.

Freeflow

I have a stock 1275. Which would be better with a twin rc40? What are the differences? I rarely see over 3k rpm.