||I am in the "Looks tacky" camp. I have Oil, Boost, Volt gauges mounted in the speaker slot and a knock meter in the clock slot, still requires taking your eyes off the road.
Jim Selin and I are both using this brand/style of knock meter. It is accurate, I have had it verified on both JWT's and SZ's dyno's. It uses the stock knock sensor and it has an audible alarm when engines sounds get into the red range.
I had a hard time finding mine, ended up locating one in Ireland about 10 years ago..