I'm not much of a tea drinker myself, but I make it for my wife, the Quooker tap dispenses water at 100°C which I believe is sufficient for tea, I can brew it quite dark and it keeps a good temperature after adding milk.

As for pre-heating, I tend to use it to pre-heat my wife's tea mug and my coffee cup before I brew with the espresso machine in the kitchen, by filling it part way for a few seconds and then pouring away; mostly to take the chill off, as our kitchen can be cold in the mornings.

I know there are lots of other cheaper brands but my understanding from researching several of them a few years back was that many/most of the cheaper ones won't keep up with the Quooker, won't be as reliable, and likely won't have the after sales support as a product from a company that specialised in that single product. There are the office ones you speak of but they're been weaker performing in my anecdotal experience of our office, and often come with service contracts.