thanks Bob , for the realistic answer...
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Short answer....yes you need arrestors.
I've done two houses in PEX. Copper valved, home run style manifolds.
The first house (2 story, 2 bath) had arrestors at the service entrance, at the input to the cold water manifold and at the washer. At first I figured I could slide on the need for arrestors for the two toilets. Once we started using the new system, it was clear that at least the upstairs toilet needed an arrestor. Luckily I had access to the upstairs toilet plumbing (in an attic) and could easily add the arrestor. I added it and the hammer noise when away.
The downstairs toilet only had a very short run of PEX from the cold manifold, which itself had large SS bellows type arrestor. IMO, the short PEX run to the toilet combined with the manifold arrestor prevented any hammer from the downstairs toilet.
On the second home; one story ranch, 2 bath ....we put arrestors "everywhere"....kitchen cold, washing machine, all toilets......no hammer.
I would suggest the same arrestor usage....... unless kitchen or bath faucets are single handle style. Single handle faucets can be shut off quickly enough to cause hammer. Even two handle faucets can be shut off quickly enough to cause hammer if one makes the effort.
If that is the case, I would suggest the use of arrestors on them as well.
cheers Bob