Namura pistons are made by ART, the same as OEM for most manufactureres, no? Namura just coats them. The coatings are ok, many OEM's use them in cars nowadays. I wouldn't pay extra for the coating, though. The piston rings seem to wear out well before the piston skirts so you would see minimal benefit of a longer piston skirt life. As cheap as I am with everything else, I still use Wiseco pistons.
To anybody who is breaking skirts off of pistons, they're either running them well beyond their service life or their piston to cylinder clearances are way to wide. Forged pistons like Wisecos are more tolerant of loose clearances, but cast pistons hold up ok when everything is set up properly.