Worth every penny
I have a pair of Fizik R3 shoes that fit quite well, but I was having foot pain on longer rides. My feet are pretty normal, if a touch wide, but my arches have gotten fairly high after a few years of wearing low-support/minimal shoes. I dropped these insoles in, with the highest-support attachment, since that's what I use in my Giro mountain shoes. I rode about 50 miles in them today, with virtually no foot pain.
The arch-size inserts attach using a double velcro, and I've never had it slip in my mountain shoes, and don't expect it to in these. You can trim them to fit fairly easily by matching your shoes' insole to the Giro version, drawing a line, and getting after it with some scissors.