Do I need a lead-free water hammer arrestor for washing machine?
If you are concerned about saving money, get the "not lead safe" one as this is a non-potable water installation.

If you are paranoid about lead and the remote possibility that a significant amount of lead could backflow from the cheaper arrester installation into your drinking water then spend the extra money on the lead-free certified product.

This is, in my opinion, an example of warnings gone awry where the actual danger is so remote as to be implausible.  I doubt that the less expensive product contains any lead at all but if you feel the need to be 100% certified then why are you quibbling about a few dollars?