Is this even legal?

I know the EU has an anti-price discrimination policy based on location, so that probably does not apply, but I don't think they thought anybody would be crazy enough to do this.

Calling it a 'System Surcharge' seems highly misleading and one of the things the EU tends to come down on like a ton of bricks is misleading line items in service charges. If they had called it an 'adblock surcharge' they might get away with it but this seems entirely on purpose.