Crucial sells this kit as CUDIMM rather than the more common UDIMM — a newer DDR5 module standard that adds an on-board clock driver to help reach higher speeds reliably, and it's the form factor here that matters more than the brand name.
Both listings in this family are rated 6400 MT/s at CL52, and the difference between them is purely how the 32GB is built: one uses a single module, the other splits the same total into 2×16GB. Because CUDIMM depends on platform support for its clock-driver feature, confirm your motherboard and chipset explicitly support CUDIMM before buying — it isn't guaranteed to behave like a standard UDIMM in every board.
There's no ECC or registered variant in this range; it's a consumer desktop part built for systems that support the newer module type.