As a new comer to the FL2 I was shocked to find out from another owner the cost of a new mirror so went looking for some kind of mirror guard/protector. What I thought would be a popular item turned out to be a very limited choice.
The only type locally available were the black plastic, self adhesive pre-formed shape which did not want to bend around the sharp curvature of the mirror casing. When warmed up they did but pealed themselves off again when they cooled. Basically the adhesive was rubbish so I removed the remains of the adhesive and used a good quality double-sided tape to re-attach them successfully. Adorned with a strip of white reflective tape I had lying around improved the looks.
Do they work? White van man tried out the driver’s side mirror protector yesterday. A loud bang and the mirror glass was out and dangling on its wires and a large score mark was on the protector but otherwise the mirror and the mirror glass were intact.
I can't say whether the mirror casing would have been broken without the guard but it would have been heavily marked at the very least.
A liberal application of Araldite and the mirror was back in place and a drop of T Cut on the protector got rid of some of the scratches.

 Freelander 2 i6 3200 Petrol
Honda Silverwing maxi-scooter (600cc)
Honda XBR 500 cafe racer