They are interchangeable.

Old 2-piece style - if the ball joint fails, it can be replaced alone

- extra piece leads to another failure point, as such, the older 2-piece style does not last as long as the new style

- a pain in the butt to replace only the ball joint (part availability, special punch tool required)

New single piece - lasts longer then the older 2-piece style

- same price (no price increase for arguably better product)

- plastic dirt guard in the space prevents splash up of dirt and water from hitting suspension and steering components that ACTUALLY WORKS!

- thus prolongs longevity of suspension and steering components

- sturdier design increases weight, decreasing feel and handling minutely, while also providing less deflection, which increases feel and handling minutely in turn

Basically, the newer design will last longer. If you have the old ones still, compare the old one with the new one, and you'll see exactly what I just described.