not personally, not yet anyway. I can't drop that kind of cash all at once on my rig, the soon to be wife would kill me. I have seen their products in action though. I know they make a duece wheel disc brake kit so you can scrap the drums or pinion brake or whatever you have. they make a kit to use 5 ton outers on dueces. they make spools. they make replacement shafts and joints. I've never seen or heard of their stuff breaking.
If you're worried about breaking shit on a duece i will say this, its cheaper to start with the 5 tons than it is to build a duece as strong as one, and then you can beef them up too!