Metal Hot water bottles

I came across these and realised the life expectancy of these would be great
webpagemetal hot water bottle

So is the zigzag shape of the top what allows sufficient flex to accommodate the change of volume as it cools?

I wonder how easy it is to open after it has cooled.

I had a certain amount of trouble with a rubber hot water bottle leaking around the cap, so I use a rice pack heated in the microwave. There are benefits of hot water, particularly if we've had a power failure, so I'd be willing to consider a metal one, but would want to do some more research. It certainly wouldn't be flexible the way my rice pack is.

I guess follow them up.
They have been on the market for many t=years I understand, the corrugation shape would also be a strength to resist crushing.