Didn't know I needed it until I had one
Just great to have my coffee and tea a constant "perfect" temperature from start to finish. My old insulated mug would keep coffee hot (initially too hot for too long), then as liquid was displaced by cold air, it would cool considerably.
This mug is best used without the companion app (works straight away right out of the box). It is a set-and-forget proposition: just add hot liquid and it turns on. Within seconds of taking your last sip, it turns itself off. Depending on your room temperature and preferred drinking temperature, you will get anywhere from 45 to 90 minutes of battery time, and essentially unlimited time when kept on the charging saucer. The mug uses 10W to charge, or 40W while actively heating. It reduces charging when hot to prevent stress on the battery, which is not user-replaceable.
The iOS app (haven't tried Android yet) is great when it works, but does add steps and fussiness. The presets are handy if you like to enjoy beverages specific temperatures. It can help you keep track of caffeine consumption as related to heart rate and sleep patterns, and you can get a nifty push-notification when your beverage has cooled to your preferred temperature (usually takes about 5 minutes or so), helping you not forget.
Love the satin surface texture and easy cleaning. It seems to be oleophobic as well, resisting fingerprints and water just beads up and runs off. This is good since it is hand-wash only (although it is water resistant).