What kind of "fails" are we talking here? He does have a note about some garbage text getting generated if you use it as a source to something else.
I think the problem you're hitting when trying to use this in the source of a query (as opposed to using the results as the source to another query), is the code doing this:
"SELECT " & strField & " FROM " & strTable
If strTable is, in fact, a physical table, then nothing stops you from running the above statement. However, if strTable is a QUERY that is attempting to in turn call "SELECT ... FROM strTable", then you enter in to an infinite recursive loop. This is because your query must call ConcatRelated() to return any results at all. ConcatRelated() REQUIRES the ability to query the underlying DataSource WITHOUT the concatenated field present in order to return a result. When you're doing this from a query, that query does not exist without the concatenated field.
Make sense?