While I have used both the ROK and the Rossa, I was never able to get consistently good results from the ROK. I accept that this was possibly due to the grinder I was using (porlex) or something else I wasn't doing quite right, but my Rossa experience has been completely different. The ROK has been sitting in its container in a cupboard since I got my Rossa.
I have a Rossa PG paired with a Rosco grinder. Both have been used daily in all sorts of conditions at home and when camping for the last 3+ years - a pretty good indication of how happy I am with the coffee I get from this combination.