Yes. 'It has a low growl with the plug installed, if you want it loud remove the plug and its has a real loud and throaty sound. It does feel like there is less lag when pushing on the accelerator. I didnt get the tuner, but they are having a 15% off sale this weekend and may look into picking it up.
Yes, It is an opening. They include a plug for it which I use. According to the manual, that opening is there for more performance gains. I will say this, with the plug removed it is really loud and throaty. Didnt really notice any difference performance wise from the plug in or removed.