On my first front caliper rebuild, I took a piston in worse shape than pictured to my Honda dealer. After the counterman told me the price of a new one, and watched all the blood drain from my face, he called the mechanic to the parts counter to have a look. One glance at it, and he said. "It looks brand new, reuse it!" (Lawyers might drool over potential liability suits. But, I think all they would gain is a dry mouth.)
Anyway, I did reuse it, and that was well over 15 years ago. The front brake caliper has never leaked, and after I switched to S.S. braided hydraulic lines, will squall the front tire if you squeeze the brake lever hard enough. It's a 550 with a big Jammer fairing on it.
I can't see any compromise in brake performance by reusing the old caliper piston in the condition posted.
Having said that. I already bought 5 of those Phenolic pistons from Kevin for eventual use in my fleet, as I have a couple pistons corroded beyond service life (determined by the amount of seal distortion in large corrosion pits). The bad ones don't leak, but they do drag because they won't retract properly. I haven't actually need to install any Phenolics yet. But, I see no reason why they wouldn't give a lasting benefit due to their anti corrosion characteristics. And, they were cheaper than any other replacement I could find. I do NOT expect them to improve brake performance. Only brake durability with time. So, they may be better brakes in the long term, but probably not in the next 5-10 years.
The high brow argument of spending max money on brakes because it is "safer", is a hollow argument without any reasonable fact to back it up, in this case. Spend your money where you wish, if it makes you feel good. If laying a guilt trip on someone else is your thing, I don't see a real benefit to either giver or recipient.
If spending money is the only criteria, then those SUV drivers must be better than the econo drivers in commute traffic too, right? Perhaps that's an ideal shared by Harley drivers? More money = a better bike?
Cheers,