I had a crack in the lens of the first set of driving lights I put on the bike. After the replacement expense I purchased the shields from EC. Later after reading how Fred H. mentioned how the amber lens brought more attention to the on coming traffic, I installed the amber lens. Glad I have the lens, they have LOTS of pitting and one is cracked a little. I feel it is all from debris being thrown up from the road.
Two ways to mount the shields I have, silicone around the edge or drill holes in the cowl and mount with the tabs. I chose the latter and have had no problem. Also, the holes are not noticable. I did need to taper the light side edge of the lens to prevent chaffing and make a better fit.
Cleaning is a little more of a chore, but the drilled hole version is easier than the silicone secured (I think).
I would replace them if one was broken or lost. I think they are worth it.