I suggest gaffer taping a plastic or cardboard extension on your screen first. See how it goes and if you think the outlay for the Touratech extension will be worth it. The B&Q gaffer tape also comes off again without leaving a sticky residue!

Relying on somebody else's judgement is no good because they won't be the same height as you or sit with the same posture.

I've tried the plastic extension trick and would buy a Touratech extension if it was �20 but it's not worth what they're asking. I find that it doesn't improve things by much but I'm only 5'9" and probably get some benefit from the existing screen that taller folks don't get.

Edit: Probably not a B&Q in Barcelona but I'll keep the reference in as it may be useful for others.