In our long term, extensive testing the reverse side of the rotor did not prove to be a concern. Between the OE dust shield acting somewhat as a splash guard when rinsing down your wheel and our mister sprayer head providing heavy coverage along the edge of the rotor (minor drip over the backside of the rotor), we have not shown any initial "rust dust" from the back side of the rotor.
The rear side of the rotor does not provide any additional dusting above and beyond typical normal usage. I'm sure Nick can attest to this in his testing as well as our other resellers and satisfied customers. :dblthumb2:
I'll make a deal with you naruto and silverfox, I'll send you both a bottle of Rustopper to even prove it. If you're completely satisfied, we'll work out payment, if not, then no cost to you. Eitherway, we are eager for your feedback.