I never saw the value of putting the stickers on, so we don't use them, but I'm retired. Most HOV lanes are open to two or more people in a car, and except for high volume traffic during "rush" hours allow full usage. As one who drives when I want, I just go when the HOV lanes are open to anyone and never have a problem. If I started work in San Francisco at 8AM, I'd need to use the freeway and drive in the packed traffic, or buy a sticker for my car and drive in the near empty HOV lane. After 10AM, the sticker is not required. Same holds true for PM traffic. Many companies allow for flexible hours and people arrange work schedules to coincide with traffic.
It's far less of an eye-sore than a front plate.