The expression is used mainly in conversation when you are about to introduce a topic that you find a little unusual or surprising. So you could be talking about someone with other people and the others are all very critical and you start to speak and say: ‘Mind you, you must agree that he works very hard.’ In that way you are expressing a different opinion from what the others are expressing.
I think Mr. Alan Townend has accepted Answer (d), disbelieving, as the correct answer in his reply to Thinker:
However, the current answer is Answer (a), unbelievable, according to my following test result. Could someone please make certain of the actual answer, unbelievable or disbelieving, and explain it?
Answer 10
correct sentence:
Mind you I was surprised because you see I find it quite unbelievable why on earth she didn’t marry me.
‘Mind you’ is one of those expressions used in informal writing or in conversation. It’s something like ‘on the other hand’ ‘i have to say’ ‘I must admit’ and so on.
Look at this:
A It’s amazing how much a doctor can earn these days, isn’t it?
B Yes, you’re right. Mind you, I do think they work very hard for their pay.