I have had a few mug warmers over the years and this one truly *does* not only warm mugs, but also keeps the contents warm for a very long time. It is quite a powerful wee machine and so far, after my initial try-outs - to keep drinks warm - I have never needed to use the maximum heat setting. Instead a mug of tea or coffee stays at a very good "drinking temperature" on the lowest setting for as long as necessary. I have never so far needed to reach the 4 hour cut-off safety period.
The *only* drawback - not really a fault, but a thing to beware of - is the switch: It is touch sensitive, just like on a smartphone or Tablet screen and one must be wary of accidentally switching it on simply by brushing against the switch. I have taken to switching it off on a switched socket I have it plugged into after a couple of times accidentally powering it up. (Mind you, at the same time, there is a very bright light to show that the warmer is switched on and also the setting which should immediately warn you of an accidental switch on.) The settings themselves seem to be very accurate.
All-in-all, it is "Almost Perfect"! I would have preferred a more "physical" switch but I can live with the warmer as it stands. (And a bonus by-the-way: One night when lying in bed and fancying a warm snack, I tipped a small tin of beans into a flat-bottomed enamel mug and switched the warmer on to full power. Whilst not having the same power as an induction plate, of course, it certainly heated my baked beans up in a reasonable time with a stirring every few minutes. Perhaps it is an answer to "High Energy" prices!)
Like I say, "Almost perfect", and I think I will get another one to sit by my armchair.