Ersatz used in English?

Hi, It just occurred to me that the German word ersatz is also used in English. How popular is it? Would an average English person know how to use it correctly and how exactly is it used anyway?
As ever thanks in advance.

Hi Nicole,

The word is not widely used and it would be limited perhaps to a metaphorical use in say a literary column but then I find it difficult to distance myself from the word because before I did national service and then went on to university, I spent some time in Germany and well remember drinking ersatz coffee. Mind you I’m talking about 50 years ago now! I think if you used it in general conversation in Britain as an alternative to substitute, you might not be understood.