Hi,
we have had a Thermos SS flask for years, very happy with it.
Others (arcosteel etc) are ok, but I now won't get one with the pop-open tops again.
They are difficult to clean, the rubber seals are flimsy, and they are prone to leakage.
You can get a bit more insulation by wrapping them in a towel; yes, it does somewhat defeat the purpose of buying one, but wrapped in a towel and stored in a gumboot or similar will keep them hot for considerably longer.
cheers