I've installed a couple of SKS fenders, and one set of Velo-Orange metal fenders. Both of the SKS took me about an hour to install. The VO took more like 8-10 hours for me to get the pair on.

SKS: How does this fit? Not intuitively obvious, try it this way, that way, looks like it'll fit, put it all together, cut the stay, round it with a file. Repeat for the front. Done. Sweated it for an hour in the garage in the summer, go get a cool drink. Go for a ride.

VO: Take off wheels, temporarily install fenders, put wheel on -- oh, it doesn't fit, run the fender out on the stays, try again -- OK, take the wheel off, screw it in one attach point, but the wheel back on, how the #**&%! did the fender move that far? Lather, rinse, repeat. OK, mark the hole, drill it, remount fender, put wheel -- dang it, it doesn't fit! Take that bolt out, loosen the stays, put the wheel in, everything is locked in, mark and drill another hole, off with the wheel, off with the fender, drill the second hole (!), put it all on, crikey, the last time I cut the fender stay to miss the rack mounting bolt I cut it too short. Take the fender off, pull off the stay and replace it with the "front" stay, leave it long, put the fender back on with stay attached loosely, install the wheel, how long can I cut the stay and still clear the rack bolt? Cut the stay, tighten it down, it's rubbing against the tire, pull the stay out as far as I can, just barely fits around the wheel. It's now mid-afternoon. Order a replacement stay, ride with the old front fender until it breaks up (another 6 months) and try again.

Results: The VO looks nice and shiny, and the extra hole is hidden beneath the rack. Sort of. The SKS fender replaced by the VO lasted about 16 years, so the one on the spare bike should be good for another4-5 years, and I've got a spare SKS fender set waiting to replace that one if/when it breaks.