My take on these bearings is in my review.

http://www.rcbearings.com/16001c-12x28x7-ceramic/

I looked at Boca and RC-Bearings. Boca was $40 for the same bearing that RC sold for $11 but it had a plastic retainer. A YS has 4 bearings but I only needed the rear bearing. Both Boca and RC had sets of chrome steel. On the web sites Boca on the single bearing reported back order until you got to ceramic and RC did not list anything other than ceramic.
I wil certainly still buy from RC Bearings but by phone and not on the web site. That way I can ask for chrome steel balls and bearings with non metallic retainers.

Denis