"So, I bought a pair of these mirrors. A flat one for drivers side, and convex for passenger side.
Bottom line is that I think these are a very good product, and well worth the (relatively modest) price.
I was a little concerned about how well the mirrors would stay attached. In fact, on my first use one came adrift - explaining why they have little tether cords. No damage to the car, even though it took place on the freeway. Was a bit exciting having that thing bouncing around in the wind.
What I learned was that you need to have the original mirror really clean (no oil or dirt), and even put a bit of spit on the suction cups. Then place the suction cups firmly on the original mirror, and crank the knob down about as tight as your little hand will go.
They go on in a slightly different position every time, so I use my mirror/seat memory for the No. 2 driver to remember the proper position for each trip.
These mirrors are small, but properly adjusted they really improve your vision to the rear, such that you can pretty much always see a car that is following. I tow a 7' wide by 12' long trailer and it really helps - especially after dark. Makes towing a lot safer.
Couple of cautions. Suction cups are rubber, and are susceptible to UV damage, so I don't think you'd want to leave these mirrors on the car for long periods. I also use a drawstring bag to keep them protected when stored in the back of the car. Finally, it's not a bad idea to label the mirrors. The convex mirror is not so convex that you won't get them confused. I put a little label on the base, with a "R" and an "L" so I don't have to think.
If you're all the time driving a duallie with a big horse trailer, then spend the money for some really big mirrors. If you're a "weekend warrior" like me, towing a racing kart trailer with my SUV, these really do a good job."
What is your level of technical expertise? Professional