The good is that they are pretty strong. The 14bff rear is pretty much bombproof and the D60 front is pretty stout even stock. The D60 is also very $$$ if you buy it by itself. $1000 or more is normal for a D60 in stock form and ok shape. In stock form the D60 can handle 38-40" tires pretty well even under hard use. There weak spot is the 30 spline stubs and hubs. They can be upgraded to 30 spline chromoly or 35 spline and you have an axle that is good up to 44" tires under heavy use. It still might break but it is going to take some work to do it. A 14bff is good to 44's stock.
The downside is they are HEAVY. They are both about 550 lbs each. They also have less ground clearence then the lighter stuff but that is the tradeoff for having alot stronger axles. You can shave both axles to help with ground clearence.
Harley