The only issues that I have heard of (from the forum across the street) is that SOMETIMES you have to replace the ejector when switching from .40 to 9mm.
Of course, you know that you need 9mm magazines, too.
I've read and heard many good things about Lone Wolf conversion barrels.
Personally, I would use this set-up at the range, but, I wouldn't use it for defensive purposes. (Again, that's my personal preference!)