The 12-sided bezel is based on a 1930s prototype Panerai used as trial pieces by the Italian Navy, which was fitted with a bezel that essentially replicates the screw-down case back. That way, both the front and the back became watertight - something important to underwater combatants. Some of these earlier Panerais had rounded front bezel, while there also existed examples with the 12-sided variant with engravings (you can find a blog post on this here), just like what we see in the new PAM685 and PAM687.
Flipping the watch over and you'd see the Panerai in-house caliber P.3000 (and also the same "bezel" as the one on the front of the watch) with a 72-hour power reserve thanks to its twin barrels. Finishing is as usual decently done, but not too elaborated as to projecting a vibe that's incoherent with the practicality and ruggedness that the watch channels. The PAM685 and PAM687 even come with a spare Plexiglas crystal, just in case you're in the mood for something truly nostalgic. Susceptible to scratches? Sure. Is it a clever move by Panerai. Absolutely.