This function could be so helpful and is incredibly tempting within the list of functions, except that it is dangerously misleading by only applying to "the current user" not across multiple users within a hosted file.
From the screen shot below, it is clear that one record is open but Get(RecordOpenCount) returns zero as we were checking the functionality within a controlled test with 2 of us accessing the same found set within the same context.
The risk of using this is further increased as some online FileMaker Help documentation does mention that it only applies to the current user (v17 help): FileMaker Pro 17 Advanced Help whereas other documentation does not (v12 help): Get(RecordOpenCount)
Unless a user has multiple windows open, we don't see a use for it?
Please be careful.