Got my Aitor Castor mediana a couple of days ago. Been carrying it and I must say the jury is still out on this one...
What I bought it for was its expected sliceyness. It excels at that! Food, paper, cardboard, you name it. This little fella almost doesn't get any resistance while cutting. That is if you sharpened it, because it wasn't so great OOTB. But hey, that's pretty much like an Opinel, they often need some touching up as well.
It's quite a bit heavier than an Opi because of the steel liners. That does give the knife a more hefty feel and maybe in a psychological way it may cause you to trust it a bit more. In short: you feel it's there in your pocket and I think that's a good thing. Some knives way so little that you forget you're carrying them.
The blade does favour one of the liners, one of the pics above shows that very clearly. As long as it doesn't rub, no biggie.
What kinda annoys me is the strong pull. There's no nail nick or anything, so you have to pull on the blade. The blade can be slippery from time to time and the pull is so strong that it slips out of your hands and that makes it very difficult to open sometimes. I hope the lock wears out a bit, that would do the knife a bit more justice. I love it, but I find it a bit difficult to operate, that's pretty much my conclusion 'till now. But for the $$, I'd say get one.