I wonder if there are many respectable companies that don't allow you to post benchmarks. It's almost as if they don't have any confidence in their product that they have to resort to such extraordinary measures.
* more about DeWitt: https://en.wikipedia.org/wiki/David_DeWitt#The_%22DeWitt_Cla...
* an overview of database licenses with such a clause today: https://stackoverflow.com/a/12116865/1376005
* an essay discussing the legality of such clauses, with links to further material on/about them: https://www.dwheeler.com/essays/dewitt-clause.html