Should I feed it back into exhaust or out on it's own, just worried how loud it will be for drive by track meters

they are very loud, but you can add a separate silencer if you want but i have always plumbed them back in. what engine is it?

1600 zetec se, although suppose I won't be lound until wastgate is open

yes, it only gets loud when open, but it will start opening earlier than when full boost is reach unless you have the gain on the boost controller turned right up which sometimes makes it difficult to control the boost as it tends to spike unless its allowed to open gradually. On track you find it difficult to not use full boost unless you know where the microphones are and come off the power as you past them.

I dont know what it would sound like on your engine but on mine it wasnt a nice sound, its very raspy. Just make sure if you plumb in it you make a nice smooth transition into the down pipe and not just T into it as it needs to flow and if it doesnt flow very well you can boost creep.