I remember when I was first shopping for a mortgage it was something that sounds like an Offset Mortgage that I was looking for - where you can overpay and underpay as required, plus offset savings against interest.

Seems like they're becoming more popular as well:
BBC NEWS | Business | Offset home loan numbers 'surge'

Anyone here actually have any experience with offset mortgages?

No I don’t because I rent. Sometimes I just think it‘s easier to rent because if you add up all of the expenses of a home, and the amount that you have to pay, that adds up to a whole lot of money that could have been invested in something else.

These days the different between the rental and mortgage payments are pretty similar - and there are few things better to invest in than a family home, both in financial and mental terms.

2c.

I am not sure what the advantage would be with an offset mortgage.

Paying it off faster, without tackling higher interest rates, for starters.

Well we can prepare for a generation of people who screw this up. It will take at least that long for non financial people to figure it out.