I've tried both the glass and plastic OI lenses, and compared them their volk counterparts. In general, the glass OI lenses produce similar images to that of the volk lenses, but for the price of the OI glass lenses, you can find a volk lens or volk super series lens (such as the superfield, or superpupil) for about the same price.
I find the AR coating to be of a much higher quality from Volk. OI's is ok, but no the best.