What always got me about the Seventh Day Adventists is the following:
1) They came out of a clearly bogus religious movement in the nineteenth century (i.e. Miller’s Adventist movement in which he mistakenly picked the date of the end of the world - more than once!).
2) Seventh Day Adventism was founded - not by Christ - but by a woman: Ellen Gould White. And her writings have, historically, been put on a par with scripture by SDAers. Modern day SDAers may be moving away from this.
3) The SDA’s often rabid anti-Catholicism is simply nonsensical and often obsessed with numerology and “hidden symbols” (often imagine).
Unfulfilled prophecy is what debunks the Jehovah's also.