The Adventist Church loves to appeal to the late, great Christian pastor and apologist Walter Martin who, in his classic The Kingdom of the Cults, only included the SDA Church in the appendix as not being a cult, but heterodox.
However, this is not the full picture. Martin had the wool pulled over his eyes by the SDA delegates sent to discuss Adventism with him for his book. He caught on to this after his book was published and he began to reinvestigate his stance. The SDA Church’s position regarding Ellen G. White as the infallible interpreter of scripture is what caused this reevaluation. The evidence of this can be watched here from his 1985 appearance on The John Ankerberg Show where he discussed with the then editor of the Adventist Review, William G. Johnsson.