On PH, you will have an open community, eager to see and test new things, so will be easier for you to find and refine your product and value proposition.
On Facebook, you will find the real public, and you will be able see if there is market interest on it (same for twitter, and Google Ads or Linkedin for B2B).
Both can be so useful, depending on he moment and what you are trying to see.
Without spending money on FB reach and not having huge fb page following, PH is better. I find FB reach algorithm to be really greedy and does not even reach to people liking/following the company page. PH is also more relevant platform as many of them makers themselves or interested in hunting new tech products.