I don't have much more to add to the existing reviews except to offer a comparison between the stainless steel mug and the plastic one Primus also offer.
The polycarbonate one (also Primus and identical in appearance, style etc) is much cheaper and unfortunately cracked after my niece and nephew got hold of it when I wasn't looking and dropped it. I have to say it was quite solid feeling, but had obviously become slightly brittle and cracked around the collar after 18 months - possibly also caused by me overtightening the lid? The stainless steel version is double the price, but will be much more durable and will keep dirnks hot for much longer - more like 2-3 hours rather than 30-45 minutes as i experienced with the plastic one. The walls also became warm with the plastic one, but don't with the stainless one - a potential hazard as you forget just how hot the contents might still be!
My only criticism would be that most of us would already have arrived at our destination long before the liquid is cool enough to drink, although it will serve me well for long journeys and in other applications, such as a half time drink at the football.
I think I would recommend the more expensive stainless version as it will no doubt last much longer.