When the PPL Confuser first appeard it was a direct copy of the actual exam questions; the author actually obtained tacit approval from CAAto publish it; the person involved had never seen the PPL exams and didn't recognise the questions!
As for watermarking, very simple to remove, the CAA can't even afford maps, so I doubt they would move away from batch printing.
The answer is clear, publish the questions, that way the quality can be monitored and if prospective pilots learn what they need to know surely that is better than answering meaningless questions of dubious quality.