Because you are fixing symptoms (w/ another failure point) with local solutions and not the disease (high pressure, bad or unsupported pipes) and good plumbers

Because you are fixing symptoms (w/ another failure point) with local solutions and not the disease (high pressure, bad or unsupported pipes) and good plumbers do not do that because A) ethics B) liability If your question is can those gas piston water hammer arrestors protect fixtures-- sure, I mean that part is just physics. Whether it's worth it before a hosecock is a completely different matter -- also as per the OP you're far more likely to break a toilet valve just from handling than from water hammer.