Hi Sara!
This expression can be considered a bit outdated to some, mind you, it’s still quite commonly used in British English across the UK and wouldn’t at all be considered disrespectful if used ;)
On my side of the pond, it’s actually very normal to use this expression, often being used to add contrasting information to a previous point made. E.g.
“I do like going to parties, mind you, they can get a bit loud and crowded - Not sure I’m too fond of that part!”
Here you can see the second statement contradicts the first but also adds a bit of extra information to what I’m saying.
Another way of saying ‘mind you’ which is common (at least here in the UK) would be ‘that being said’. E.g.
“I do like going to parties, that being said, they can get a bit loud and crowded - Not sure I’m too fond of that part!”
Much like ‘mind you’, some people might consider this expression to be a bit old-fashioned, that being said, they’re both a big part of my own vocabulary and I’ve never been pulled aside by someone for being rude or disrespectful when using these!
I hope this gave you a different perspective on the use of this expression. Happy learning :)