The WiFi is expensive (€9 for an hour, €29 for the whole flight), but at least it worked well. In the other planes it was equally expensive but you only got a ridiculous data limit (something like 25MB), which is why I was mentioning it in my post. I don't think I'll ever pay for it at those ratea but in this occasion I paid for one hour out of curiosity (to see if it really had improved). I was pleasantly surprised in that sense and also because you at least get to load Iberia's website with flight information for free, which seems something that is actually useful.

I find it strange that you kept sliding off, since these seats seem to me to offer more friction than the old ones, perhaps you were on the A333?