I use this mirror for touring because it provides a full scale, accurate reflection. All others I have found represent vehicles as farther back, faster moving and more difficult to pick up. If the bike falls the mirror will usually be broken so the trade off is that some others are more durable. I carry a spare and buy a couple when on sale but the crystal clear accuracy is well worth it on the open road. I have ridden across the country 7 times and this product is as important as the right tires.
My club mates insisted that I get this mirror if I were going to cycle in a pace-line. Frankly, I was hesitant. Now that I have it, I've become dependent on it for safety and security. Further, I can call out the Car Back warning when I am riding at the tail of the line and I can see that we are All In. I think it's a necessary.
This product will not fit on a bike with a Dura-Ace 7900 hoods. The end that you are supposed to attach to the brake hood is too curve to wrap properly around it. It's too bad because the rest of the product looks to be well made.