I love this mug! Despite the one negative review on this version, I based my decision to buy this on reviews on other models of this mug.
As long as you don't press the button (Duh!), it's absolutely leak-proof, keeps your beverage HOT for hours (it's drinkable for me after 1.5 to 2 hours!). I put it in a little plastic-bag with a clip in my handbag....NOT upright and the bag is ALWAYS dry!
Of course you have to be careful not to fill in too much liquid and also release a bit of pressure every now and then (by pressing the button whilst holding in an upright position) before you throw it in your bag. The instructions also advise to let the water/liquid cool down to 90°C.
At first I found it a bit awkward to drink, as you don't have a rim as such and you have to "kiss" the mug. But this is in fact a much cleaner solution compared to the mugs I used before.
The lid should be rinsed right after use, as (as far as I can tell) you can't take it apart. The instructions say it's dishwasher save, so is the mug itself if NOT coloured (like this version is).