See this meta post too
Currently, users with <3k reputation, while flagging to close as off topic are presented with the custom close reasons and "belongs elsewhere" close reason.
However, the removal of the default off topic and Too Localized has left behind a void that is not completely filled by custom off topic reasons. For >3k users, the freeform "trolley car" close reason works pretty well (though it has issues too). However, <3k users do not have any valid flag options. In such cases they are force to custom flag (or pick a random close reason), which doesn't push the question into the queue.
The freeform close reason leaves a comment and creates a temporary entry in the VTC Off Topic dialog that is present only on that particular question. The close banner used is the efault off topic one (
This question does not appear to be about $Topic, within the scope defined in the help center.). I don't see much scope for abuse if flaggers are allowed to use this. The most that can happen is that flaggers can populate the dialog with nonsense close reasons will, but since it's only for that particular question I don't see much harm in this.