I have one in my panel, but I'll be removing it soon as I'll need the space for a Garmin G5. To tell the truth, I only put it in to avoid any argument at airworthiness time. Never looked at it in flight and can't imagine any case where I'd need it. I have 2 GPSs, one in the panel and the another that drives an iPad mini with foreflight, plus my phone is a pretty handy navigator, 2 alternators and a battery for pretty reliable power to drive the built ins.
About the only thing my panel mount compass has done for me is drip baby oil on my leg when I get up to about 12,000'. (topped the unit off with baby oil on installation) That thing's gotta go!