[wsemajb]

It's fine to use, but beware. There are English language instructors who take it upon themselves, (in my experience it was usually at the high school senior or college freshman level) to discourage use of many idiomatic expressions and popular metaphors by marking every one they find in a paper. They are not firmly against their use, but many young writers do tend to use them excessively for "color", as a substitute for style and clarity.

"Cut the mustard" is not necessarily bad usage. Everyone would understand it's meaning. But unless you were using it ironically or humorously in a college level paper, your instructor would probably make some comment in the margins. This is true of many idioms as often they are regarded as cliches. Look up the definitions of trite and cliche. That will explain this a little further.