I have a set of the Thermo's that I have been having for a little over a year. Unfortunately I was deployed for over half that time so I haven't been able to use them nearly as much as I would have liked.
Overall I think these boot compare pretty well with the Nepal EVO. The may be a touch warmer and I think are a pretty close to the same weight at 84 oz for my size EU 44/UK 10/US 11. They climb steep ice and snow very well and walk pretty darn good. The sole is nice and stiff and the fit is exceptional and highly customizable. They fit slightly wider that the typical La Sportiva fit.
I have used them comfortably down into the low teens and have had cold feet one time (at Camp Muir in 20 degree weather, exhausted and trying to boil water)
From a size standpoint my 44 Mammut's fit like my 44.5 La Sprotiva Trango Alps and my size 45 Baruntse's. In fact the insoles are exactly the same size in all three.
Hope this helps,
Ji