Like Doug "Laidoffsick" said:
- They look better. Closer to scale size than the hi-rail coupler. The 700-series look more prototypical than any hi-rail coupler produced.
- They work better. The only uncouple when you want them to. You don't have to slam into them to get them to couple.
- Because you're pulling on the car frame as opposed to the trucks, operation is more natural. You also get the "slack action" on longer trains.
There are some caveats:
- Body-mounted couplers require wider curves. You really shouldn't use them unless you have 36" radius (O-72) curves or larger.
- You'll likely have to adjust the mounting height to get them to the right height on some cars. This is especially true if you're converting hi-rail cars as some of them ride high to compensate for the flanges.
- Unless you convert every single locomotive and piece of rolling stock to Kadees, you'll need a couple of "Transition Cars".
