Somewhere on Bike Forums I've posted photos of how I secure the Take-A-Look mirror to my helmets.

• I use one of those plastic discount cards from a grocery store and cut it to fit the recesses in the softer EPS foam inside the helmet. This will serve the same purpose as the earpieces on eyeglasses -- something for the three grabbers on the mirror stem to hold onto.
• Then I'll punch a hole in the plastic card. That's the zip ties to go through so nothing slips off.
• I use one zip tie to secure the mirror to the card, with the zip tie going through the punched hole.
• I use a second zip tie to secure the card (again, through a punched hole) to the helmet, on the inside, going through a vent.
• This leaves enough wiggle room to adjust the angle of the mirror stalk/stem up and down a bit. I'll snug up the zip tie to hold the tension so I don't have to keep adjusting the mirror.

It's simpler to make that it sounds. Takes only a few minutes.

For now I have one Take-A-Look attached to my Bell Formula MIPS. The second is loose so I mount it to whatever sunglasses or safety glasses I plan to wear. That's for use with my POC commuter helmet or my aero helmet. I wear the POC on my hybrid, which has bar-end shifters so there's no handy place to mount a mirror on the bike.

The aero helmet lacks vents for mounting, and a permanently attached mirror would defeat the purpose of an aero helmet. The aero helmet and jersey are usually good for an extra 1 mph on my workout routes, especially on windy days. But depending on traffic I may wear glasses with the mirror on days when I'm using the aero helmet. When I reach my usual workout routes with 2 to 6 mile time trial segments, I'll stick the mirror in my jersey pocket and just wear the sunglasses or use the aero helmet's magnet mounted visor. If my neck flexibility was better I wouldn't bother with this setup, but it helps me with navigating traffic until I reach my workout segments. There isn't much traffic there so I only need the bar-end mirror.