>I don't what kind of impact this could have in your case, however one aspect that I consider important (and sometimes still take advantage of) is that creating an IDX file does not require exclusive use of the dbf, as opposed to creating CDX tags that does require the dbf to be opened exclusive.

That's for structural cdx only. A separate cdx can be created at will. And there's a good chance that the app to convert may contain a lot of such ad hoc indexes - that was our main tool before FP had internal SQL engine.