i use mine on open fires all the time (even been known to put it on top of the forge on more than one occasion!). Place it on top of couple of sticks/rocks to allow air to pass underneath it and watch out where the handle is sitting, but otherwise its fine.
When I first came across this type of kettle, it had an integral wind shield (ie a perforated skirt of metal) all around the base. No seperate base to lose or buckle, you just placed it over a small fire and fuelled as usual. Particularly handy when you already have a fire going, not so great if you don't want to light a fire on the ground (but then you can put a tray down first). My modern 5L stainless one has this feature too.