"Steam canners are not recommended because processing times for use with current models have not been adequately researched."
that quoted from here....
http://www.uga.edu/nchfp/how/general/equp_methods_not_recommended.html of course your primary goal in preserving food is to actually..well.....preserve it. That is to prevent spoilage and maintain a product that is safe to actually eat. In order for us to safely can anything...at home or in a business setting....proper reliable and reproducable testing must assure us that adequate temperatures have been achieved for an adequate amount of time to kill any pathogenic organisms and that the food in question is simultaneously sealed from outside sources of contamination until such time as we would like to consume it. this has apparently been somewhat of a problem for steam canners.
this talks about the controversy
http://www.canningpantry.com/steam-canners.html since water in water bath canners can be reused I have trouble seeing why to take the risk with steam canners when there is so much reliable tested guidelines and recipes out there for WB canning. it appears that the people who sell steam canners are the only ones who think they are acceptable