I've been using one of those old enameled tin cups just about forever. But it just doesn't fit inside a BOT pot or into other nooks in my pack. When I replaced it with the Vargo travel mug when packing for several recent trips, I was amazed at what a difference it made. The foldable handles allow it to nestle neatly into the BOT and just about anywhere else. (They also really resist heat transfer, so no need to use your dirty socks as a hot pad to hold your hot coffee!)
Like all the other Vargo titanium containers, it can handle going right on the coals so it also doubles as a small cook pot if needed, opening up more options for meal-making without lugging along additional cookware. And I didn't expect much of a weight difference but holding the tin cup and this one together, the difference is not negligible!