I looked, but since I dont know, I didn't comment. Uhmm, as far as I know, Sealed bearings are sealed bearings... Unless the manufacturer is known for having a poop quality product, then thats different...
If your bearings aren't sticking, gumming up, or spinning rough, then why replace them? Tho that would be good to have the backup parts, Incase a bearing does seize. You'll have it replaced right off, instead of having to go, locate bearings that fit, and buy em.
~ Mike