Years ago my father gave me an Aitor with a serrated spine, but it had no guard, right where you would place your thumb is where the serrations were.
My father was using it once, his hand slipped and those damn serrations sliced his thumb to the bone. Needless to say, it was one of the worst knife designs I've ever seen and dangerous.
Aside from it being lethal to the user, it was about as sharp as a hammer and could not get any sharper, the steel must have been hardened to 64, I'm not kidding.
That's my only experience with Aitor. I used to have a Muela as well, the small handle was olive drab zytel, blade was some kind of stainless with a slight recurve, hollow ground. It too had a serrated spine. It could get razor sharp, but did not hold an edge at all. It was only $19.99 though, so for the money it was an okay knife.