The striker they sent you appears to be the older machined style (2nd revision, with the extra metal at the front of the striker's foot, for more spring compression). This requires the 2-piece white spring keepers. The next (current) revision is the shiny MIM striker that requires the 1-piece white spring keeper.
Did you just call and ask for the separate striker, and not the complete striker assembly?
If you ordered it as an individual component, did they ask what was in your 9c (finish color) when you ordered it? If so, they might have sent you the right part for the 2-piece spring keeper design you're using, maybe? Dunno. I can only guess.
It's easier to order the striker assembly, if it's for a repair (or spare). I keep a few individual striker springs for periodic preventive maintenance replacement (every 5K rounds or 5 years of use, whichever occurs first).
BTW, I wouldn't consider the machined strikers to be "prone to breakage". The MIM revision is indeed a more robust unit (especially for competitive shooters who might want to do a lot of dry-fire), but the machined strikers weren't reported to be breaking in any great numbers. Nor were they subject to a "Recall". The engineers are constantly making improvements, refinements and changes in manufacturing specs.
The current armorer manual (3rd version, from 2010) lists both types of striker assemblies, so armorers can maintain both designs (because of the difference in spring keeper design). There's still a lot of them out there in-service and doing fine.
I ran a few thousand rounds through my pair of M&P's, both of which had the machined strikers, without any breakage. I eventually replaced mine with the newer versions to see if I could notice any difference, but I kept the original parts as spares. I had a couple extra of the machined strikers I'd ordered as spare/repair parts, and I'm keeping them for that use.
If it bothers you, you could call customer service and ask to return that individual striker (for refund, filling out the form pictured under the striker), and instead ask to order a complete striker assembly of the current MIM design (for the 9/.40/.357 model).