It does keep my coffee hot for quite a while and the auto seal lid is quite effective.  However, if the mug is dropped with the lid on, the inside of the lid can come loose.  It does not seem to be fixable and therefore the whole unit is useless..  This has happened to two of mine and is very disappointing.  The Autoseal is preferable to the newer top, however, as that one only seals by closing the top.