Take-A-Look, ditto.
I have the long stem version rigged to one helmet. And a short stem version for my various glasses -- easy to swap between glasses.
I rigged up my own helmet mount from an unused stiff bit of plastic (grocery store discount card), cut to fit a niche just inside the helmet. Added a couple of small holes. The Take-A-Look is attached and zip tied to the card, through one of the little holes I punched in the card. Then the card is zipped tied to the helmet, again through a hole punched in the card. Neat, durable, adjustable and can be redone anytime without adhesive mess.
When I first tried the Take-A-Look a couple of years ago I hated it. Felt completely non-intuitive and disorienting. So I wore it to get used to it gradually while continuing to rely on my handlebar mirror on my hybrid. Took about a month but I finally came to prefer the Take-A-Look. And I don't have a mirror on my road bike, so I rely on the helmet or glasses mirror.
Positioning is critical to making a helmet or glasses mirror easy to use. If it's too far inboard the view will be blocked by your own head and you'll need to turn your head too much to see anything. If it's too far outboard you'll feel some eye strain from looking so far over. When it's within an ideal position range it's more intuitive, and you can often see movement behind you without actually looking at the mirror.