Sometimes manifolds have more spigots than house has plumbing, see that frequently.
My concern are all those elbows, each one has two potential failure points, what’s wrong with just curving the PEX in, or mounting the manifolds horizontally? That’s what I mostly see plumbers doing.
Maniblocks were the last ditch effort on Polybutylene piping systems here in AZ. This system looks like an early PEX piping system to me, probably early 90’s.