I'm using bar end mirrors on both bikes. Big enough vibration's not a problem, and since I acquired one of TREK'S CarBack radar devices I get rearward feedback in much greater depth than with a mirror alone. Now they're used just to confirm proximity & scale, something the CarBack doesn't provide.

If Garmin's Varia (or similar) provides real-time video info to a front-mounted display (as would something like a GoPro) I'm unaware of it. That would negate having a mirror as well as removing the distraction of looking away from forward path.