If the Racepac is the slender supermodel cousin of the Crud Catcher, then the ZX is the attention-seeking slightly sexier younger sister.
With all the sculpted curves you'd expect from such a girl, this gives more coverage (and therefore protection) than the Racepac version, but a bit less than the Crud Catcher. But we're talking relatively small amounts of extra splash here.
Whichever one takes your fancy and you eventually take home will make you happy. Especially as like all the other Cruds (so to speak) this is recyclable and comes with the same secure, fast fix O ring attachment. Plus, for any bike that has bottle cage mounts on the underside of the down tube, the ZX is drilled to fit, so you can use those instead of the O rings. If you need any further convincing, this is Peaty's choice of mudguard, too...