I've been using strap on extension mirrors for the 7 years I've had my 13 Scamp
. While the Law requires vision at 200 feet, I like to see what's behind my trailer within that 200 feet. I've found they also come in very handy for a single person backing up. Simply gives you more field of vision.
The strap on mirrors do viberate quite a bit but you get used to that and it depends upon how fast you are traveling as well as wind conditions. When driving my attention it not totally to the rear, just an occasional glance. I find having the extension mirror really beneficial on the right side when making a lane change. With the Jeep and extension mirrors I have no blind spots. Even with the viberation you know what's behind or beside you.
As for having to adjust them frequently, I don't but maybe once and awhile. I've found that doing the initial adjustment for your field vision and tightening down the set screws is fine. The big item is that when they are off the vehicle you use care to store them. I store them in their own box with a lid. That way nothing can come in contact with them to cause them to be out of adjustment.
I don't use them with my utility trailer as I don't need them for vision and it sure feels funny. It's sort of like a seat belt, I now feel lost with out them.
I tried taking the gravel cover off the front window so I could see through my Scamp
but I can't. I really don't know how others do. You might be able to if you want to try that once you get your trailer and get set up.