It's just the same as a single API call with the System plug-in like this:
System::Call 'kernel32::CreateMutexA(i 0, i 0, t "myMutex") i .r1 ?e'
The only advantage could be that if you only need this System call it might save a KB or two.
Was just playing around with this plugin and observed that the routine returns a different value if the "optional parameter" is explicitly "2" vs. letting it default to "2".
CreateMutex::nsCreateMutex "myMutex" "2"
returns "MUTEX_EXISTS"
CreateMutex::nsCreateMutex "myMutex"
returns "ALREADY_EXISTS"