The opening is relatively narrow (slightly narrower than the container itself) but I feel this is not a disadvantage - you can fill with unproblematic. The purification of the product (seals, protection ...) I found no problem - you can wash all parts separately, in my experience, but remains "hanging" relatively little.
The 0.75L version is just the right size for one serving (for adults). The vessel has so far proved very dense, there is nothing leaked - I certainly have not really conveyed liquid foods (such as soup) or drink.
The Esbit Thermo container so I can absolutely recommend.