I have both bushing dies and Lee collet dies. I prefer the collet dies, will use them when available, and have actually had one made for my .284 Win., which I use in preference to my Redding bushing die.
Bushing dies work best if you neck turn, because you don't care the that outside of the neck is concentric, but the inside. If you don't neck turn, you just push the irregularities in neck thickness inside the neck. In other words, a bushing die has a level of indirection that the collet die doesn't. That said, if you neck turn, it is a great way to precisely control neck tension, and vary the amount of neck sizing. Also, I like the Redding bushing FL sizers more than the body die/neck sizer die (of whatever sort) combo, because I FL size (with the die properly adjusted via their competition shellholders for proper shoulder bump), because that saves me a step.
In a collet die, because the collet presses the neck against a mandrel, the inside of the neck will always be concentric. That actually a pretty smart design, since you don't have to neck turn for best results. This also means that if your cases are prone to forming a donut at the neck shoulder junction, the donut always gets pushed to the outside of the neck, where it won't mess with consistent bullet seating. The downside is, the neck tension is fixed by the mandrel you use. If you don't like the mandrel that came with the die, you have to turn it down or get a larger one from Lee. But in my experience, the sizes are pretty intelligently chosen. Lee made my .284 collet die with a mandrel that was 0.001" smaller than the Berger 180gr hybrids that I shoot, which is what I want. My only real complaint about the collet dies is that their finish is not as nice as a Redding die, so the collet can sometimes bind up, but you can polish the fingers of the collet to smooth them out.
As for the cap on top, if you break it, you are applying too much force. Once you squeeze the brass against the mandrel, you can't squeeze it any further. Any additional force you apply is directed to that cap, which is made of aluminum on purpose, so that it fails instead of something else more expensive. This is especially true on non-Lee presses, where the linkages can cam over for additional force.