Off the top of my head…
Usage
Saying something without preparation.
"Off the top of my head, I'd choose Tokyo."
Band 7 — Natural and flexible
Range of expressions used naturally.
Come to think of it…
Usage
Adding a thought that just occurred.
"Come to think of it, my grandfather inspired me a lot."
I have mixed feelings about…
Usage
Show nuance and balanced thinking.
"I have mixed feelings about social media, really."
Now that you mention it…
Usage
Build naturally on the question.
"Now that you mention it, I do read more on weekends."
It's a double-edged sword…
Usage
Discuss pros and cons fluently.
"Working from home is a double-edged sword."