I use the one from Morrisons supermarket , lots of cheap versions available, keeps plenty hot for 5/6 hrs but no as good as more expensive ones. So good I bought a 2nd and still use both. Not sure if they still sell this version, but if so it is great can use with one hand or gloves on too.
Very nice if a bit pricey, even if ordered from Japan (though in my case, as they accidentally sent me two, that was less of an issue!). Fits in car cup holders, you can drink straight from the spout, and keeps tea hot all day. I usually fill mine before site visits at around 8am, and the contents are still hot at around 5pm when I am driving home. Never leaked despite being thrown upside down in a rucksack. Only possible problem is that as it's tall and thin, it might not fit under the spouts of coffee machines in shops?
FWIW, Which Dec 2019 (just dropped on my doormat, no other connection other than as a suscriber) has a short review (p. 13) on reusable cups and mugs. Its top picks are:
Lorraine McCall began her attempt today at a continuous, self-powered round of the Grahams, a four-month tour of upland Scotland combining walking and bikepacking. If successful, she'll be the first person that we know of to do it.
Podcast Mountain Air - 6. Rob Woodall, Britain's Greatest Peak Bagger?
