Unfortunately it’s not just that the parylene was applied correctly, they also must be handled appropriately the entire time between manufacture and installation. Parylene C is usually used for this, and it is a monomer. It’s applied in a vacuum at high velocity, typically in layers. The monomer particles are jagged and rough, and ram together like forcing a bunch of puzzle pieces to stick together by crushing them into a ball rather than laying them out carefully. This is all fine, and works well enough, but only if nothing comes along to press on the haphazardly constructed mass with much force. Once you do, it will crack and crumble as each individual particle is jostled around.
Parylene coating was designed and developed for protecting components on PCBs that don’t encounter any force at all, but need protection against the elements (moisture, dirt, etc). For PCBs that do encounter forces (like in rockets or military jets), a different coating is used. This was never designed for anything like magnets. This is the heart of the problem with parylene coated magnets in my view. The material is so brittle and sensitive, and you’ve literally coated a magnet - a thing that is violently pulled toward other things if you get it too close. I’ve literally seen body modders with stacks of these magnets in their bags before… like, how did you get them to gently stack together on each other without the typical "click" that comes with getting two magnets too close to each other? Ah, you didn't.. you just picked one off the stack to show me, then let it snap right back to the top of the stack without a second thought.
But even if your supplier hasn’t stacked them, how could you ever be sure they didn’t let them come into any contact with any magnetically active metals what so ever? From the moment you take a parylene coated magnet out of the coating chamber, it’s a liability.
Giant cracks in parylene are easily detectable, but small any pathways which may have opened up for moisture to get in to the magnet and start breaking it down - those are not possible to see with the naked eye. Not to mention any small pieces that may flake off or abrade over time, only to be lost forever floating around in your body.
Parylene is the most risky way to coat a magnet, yet here we are discussing the safety of grade 2 pure machined titanium I can literally blast with a laser and smash with a hammer and still not breech the core…
… all because it’s not a “mirror finish”… which by the way has never been tested or validated in any way for anything by anyone… it’s just that it “feels like it should be”… but no data has ever been collected on this. I mean shit, just take a look at the most common titanium implants - hip replacements. The only mirror finish on there is the friction surface where the socket rests on the ball (for obvious reasons)… the rest is just dull grey machined titanium.
So yes, some people get lucky and have parylene coated magnets implanted that withstand the test of time, but overall the results are in - parylene is risky AF, yet professionals seem to keep using and implanting devices with substandard coatings while throwing up static about the Titan… well mark me down as “annoyed”.