I am quite fond of the Opinels because I find they are cheap, tough, and perform well. Also, at the advice of other Members, I use them with my EdgePro to learn new sharpening techniques, avoiding removing unnecessary metal from other knives that cost much more (for example, learning to set a double bevel.) They've also influenced my preference for extremely thin kitchen knives made from carbon steels with paper thin edges, both in regards to paring knives and chef knives. With an EDC folder, they've led me to favor a very thin edge (recently from S90V, Super Blue, and M390 steel as I find they can hold an almost stupidly thin edge and still resist rolling.)
Without Opinel carbon, I probably would not have tried out 52100, White, Super Blue, or rediscovered a love for the 10xx series, because of that initial reluctance that can come with carbon steels regarding corrosion. However, Opinels gave me the chance to learn about forcing patinas, and I quickly discovered that the combination of good edge holding, chip resistance, and the super ease of sharpening justified the extra attention to upkeep. To this day, I'll still use an Opinel as a paring knife and often try out something new with it before doing it to one of my pricier paring knives.
Now if only someone made inexpensive S90V folders that I could use in the same way...