My plastic fenders broke after about 18 years (SKS predecessor company). Outraged at such a flimsy product, I bought metal fenders (from Velo Orange) to replace them. It took me about 12 hours over two days, with a week in between to order and receive a replacement strut, to get the stainless fenders mounted. I'm too enraged (or lazy) to do something about the hole in the rear fender I drilled in the wrong place.
I certainly hope these metal fenders last forever. Obviously I lack the knowledge and skill to put a pair on. I have learned one lesson: I bought a set of SKS fenders in case I need to replace another set of SKS fenders. Those I can put on in just over an hour.
FWIW, one contributor here noted that when he worked in a bike shop, fender installation was a time and materials job, rather than a fixed price effort. I've seen two shops put on SKS fenders in about the same hour it takes me. I could buy a new bike for the price of T&M on metal fenders with the same skill as I exhibited.