#3
The g string is better, it stops the hum coming from your guitar and pedals and can also be setup to stop the hum from the preamp. It's basically like having a noise gate in front of the amp and in the FX loop.
I don't give a shit if you listen to me or not
#4
The expensive one has 3 outputs and the less expensive one has 1. If you just need a noise reducer I'm sure the lower priced one is all that you'll need and according to the reviews it's also bloody fantastic.