I've had the Ron Morris cable conversion kit for the last 8 years, and beating the snot out of my car the whole time I haven't had one problem. Not just no failures, but also no need to even adjust or replace the cable, or any other little issues. That's my personal experience.
But to answer your question, I've never had any experience with Mustang Steve's setup, but I've also heard a LOT of good reviews on it, mostly from here on Stangnet. I don't think I've really heard of any problems with it either.
I really don't think you can go wrong either way.
Too bad that cable conversion kits on these old cars work better than even the aftermarket "good" cable stuff on fox bodies. I've tried all kinds of combos on the 90, and always have problems snapping the cables, but that's a story for another forum.