I can't find this film, not even a trailer, online.
DVD Talk praises the acting but warns: "Even for a Pre-Code feature Kongo is a catalog of perversions not seen again until the 1970s" and says,
They don't make them like Kongo any more. Today's perverse torture porn may have the edge in realistic effects and outright violence, but it can't match the psychological malice of The Bad Old Days.10K Bullets says,
If you seek the most perverse and sordid pre-code melodrama ever made, look no further than MGM’s Kongo. It’s a quaint tale of adultery, alcoholism, forced drug dependency and prostitution, voodoo, human sacrifice, sadism, rape, madness, murder and revenge.TCM has has an overview and a succinct plot description: "A crippled madman seeks revenge on the daughter of the man who betrayed him."