Love the concept - they keep my collar straight and upright, and I no longer have to worry about them going askew under a sport coat or due to humidity. They hold well all day, even through slightly thicker fabric.
Unfortunately, one of the magnets chipped within minutes of fiddling with them. It still works and holds fine, but it's a bit of an eyesore. I'm slightly concerned about the chip getting worse at time goes on.
I do wish that Birchbox carried the 2" stays as well, though ... they only have the standard 2.5" size which are slightly big for the Hall&Madden shirts I own.