ADATA's Premier line is the value end of its SODIMM catalogue, built for laptop upgrades rather than gaming desktops, and this particular family keeps capacity fixed at 16GB while varying speed instead — the reverse of how most families on this site are organised.
Both listings share the same 1×16GB configuration but differ in 2666 MT/s and matching CL19, so two kits with near-identical names can still be different products once you check the numbers. Confirm which speed grade a listing actually is before assuming Premier means one fixed rating.
As SODIMM, it fits laptop and small-form-factor memory slots, not a desktop board's socket — check your machine's supported DDR4 speed, since running below a module's rated speed is normal if your platform doesn't support the higher grade.