If I heard that advice, I'd be questioning the quality of advice I'd be getting from that person. From my own experience, I have not found the Varex to cause any loss in power or an increase in fuel consumption. I had a pair fitted in March 2009 (see "DJKOR's Aurion" & "GOT MY VAREX =]") and considering that afterwards I had remained just as heavy-footed... or increased... my fuel consumption figures did not go bad. If anything, they probably improvedd slightly, but that could have been many other factors. Anyways, you can see my fuel consumption trends here: Aurion Fuel Consumption (Excel Spreadsheet) My quarter mile times weren't affected as well. Actually I had one of my best runs with said aftermarket exhaust fitted (see here) but once again, there could have been a number of other factors at play. As for when the Varex is closed, I can't quite say. I rarely ever closed mine and after seeing how much of a restriction it cam be when closed, I never really liked the idea. Personally, I would suggest to save your money and just get a pair of good quality high-flow mufflers. The Varex are pretty much a gimmick.