Light Action is like the X but with easier entry and exit. Light Action and X give you 15 degrees of float. Zeroes allow you to adjust the float from 15 degrees to Zero (get it?). The mechanism for adjusting the float, two set screws, also facilitates fine adjustment of the cleat angle without removing the cleat.

Float on all Speedplay pedals is unsprung--there's no centering mechanism.

After toeclips with slotted cleats, old-style Look, and Time RXS, I'm using Zeroes. They were a little tricky getting into at first, and that unsprung float was initially disconcerting, but at 59 my brain is still capable of forming new synapses.