It is under my understanding that the voltage regulator (U7) on the PCB would shelter the PCB from any damage. I don't think the PCB would cause any damage to the console, since the console is the one with higher voltage.
I test all our games my self, beta test that is, so I have to play through them for hours on both NES NTSC and PAL consoles (I don't care about clones, most are fine with exception of Retron 5).
Im not a hardware engineer, the factory we used is not the one directly selling bootlegs on Aliexpress, they serve all china, taiwan, and hong kong. And are the only ones that really give quality components and gold pins on PCBs (thus why Retrobit uses them) The guy that designs has been an electronics engineer for over 40 years and has developed games for NES and Genesis. He has done clone consoles, NOACs, and now he is working on clone consoles with upscalers He is pretty smart and we trusted his judgement, on top of that we tested the PCB to work.
It is a shame that he does sell the PCBs to other trade companies in china that do bootlegs but oh well, we just buy the PCBs, and cannot control anything else. We might be moving to get the games done by other company that has done legit hardware products sold world wide; we'll see how it goes.
We'll look into this issue and stress test to see if the PCB causes any damages to the console or to itself by being played on the console.
Also, I am going to reach out to Kevtris to see if he can put the rumors to sleep about the whole 5v >3.3V chips killing retro consoles.