They are a nasty bunch also.

Any religion that interferes directly with people's daily lives is a cult and it does, so it is a cult just like Mormonism and most evangelical churches.

The definition of "cult" and "religion" are a bit vague. The sarcastic version is that "cult" is a religion that is too small and/or young for people to have grown accustomed to.

"Cult" is a pejorative label used by established religious people to describe a competing religion is unsavory. Some people (including some irreligious people) use the label to suggest unusually high levels of authoritarian control over adherents. But here again, how much is "high" is hard to pin down.

Some people use "cult" to describe strange or unapproved beliefs, but that is subjective and in the eye of the beholder.

Arguably the best use of the word is to describe a sect with pretenses to be accepted into (or at least as a variant of) a major religion but fails to check all the boxes that normally define that religion.

The Jehovah's Witnesses is a relatively young religion and a relatively small one. It also is relatively controlling. It also does not "check all the boxes" that historically define Christianity (generally codified in the historic church creeds). For example they are unitarian rather than trinitarian, and annihilationist rather than destructionist. As such, some of their doctrines are heretical to historic Christianity.

JWs also satisfy the "strange beliefs" criteria with their prohibition of blood transfusions and their deep suspicion of higher education to the point that they strongly discourage their young people from going to college. Among other things I've probably forgotten.

On the other hand, JWs want to be considered "Christian", given that they believe in Jesus. And they would regard their "differentness" as a correction to a lost Christian orthodoxy. In other words, they believe, as do virtually all sects, that they are correct where most everyone else is wrong.

The Mormons are very similar to the JWs in regards to all these things; they just have a different set of distinctive and sometimes "weird" beliefs, and are considered heretical for different reasons. But the other thing they have in common with the JWs is they are a relatively young sect (though older than the Witnesses) and want to identify as "Christian" even though a significant percentage of Christians reject them.