I use them on both sides of mine. Stuck on the very bottom of the sunglasses, they are just right for letting me see my computer, cue sheet, etc, but end at handlebar level in my vision, so everything distant I see without them.
On one pair of sunglasses that isn't very big, I trimmed the stick-on lenses so they wouldn't take up too much of the sunglass real estate (and would still end at handlebar level). I love the stick-on lenses, and use them on my safety glasses at work, too.