I found the Varex to be fine shut right down when putting around town, otherwise I would leave it wide open.
As birds has mentioned, even wide open it is not particularly loud, and it definitely produces a nice note - much nicer than the Xforce cannon I had on previously. I certainly wouldn't put my foot down with the Varex closed down, or even partially closed down.
You may possibly lose a few KW into the bargain with the Varex - I didn't put mine on the dyno after the change, so that is only a guess on my part.
I should add that I got the oval twin pipe version, and not the cannon type.
I certainly didn't regret getting the Varex, didn't notice any actual power loss and loved the note it produced.
Originally I bought it for situations where I didn't want to attract attention, and Varex did a great job as far as that went.