First time I got a chance to read his book, "Combatting Cult Mind Control" and was interested to see if JW's fell into the cult mold. My opinion after carefully reading and having left the Witnesses after almost 30 years is... no, they don't. However, I would add that they wish they were but are simply too big and unwieldy to really pull it off.
I think its an interesting case because very little of the physical cult experience described in the book fits a typical witness (no physical isolation, no sleep deprivation, no public humiliations, they don't seem to have the right type of money hungry charismatic cult leader, no constant fundraising efforts, no chanting/hypnosis/etc, etc etc. Reading anyone of the many case studies in there fits what I would generally have pictured as a cult. The Witnesses don't fit any of that.
However, its also the case that most of the mental aspects of how a cult gets people into their drapped physical existence is very similar to the Witnesses, if not exact (attempted information control, attempted behavior control, attempted emotional control, attempted thought control, no acceptable exit, guilt/fear tactics, etc etc etc).
But ultimately, the Witnesses do NOT have physical control over their members. Most members still go home and spend about 160 of the 168 hours of the week on their own away from the group if they please. Now at best, the GB sends out the message trying to ask or guilt people into behaving like a cult member in the 95% of the time they are away from the Kingdom Hall, but thats impossible. Witnesses are too free and outside direct control that asking them to control it all themselves is, for most, a losing battle. They're trying: higher education, friends, workplace flirting, TV, video games, music, sports, clubs, Internet, dating, movies, sex, alcohol, drugs, and on and on. If they had a way to actually control all these things they would probably do it, but its not feasible with such a large group. Some people take it all in and burn themselves out police themselves, but almost every Witness I've met is willfully failing at being controlled in some of these aspects. The traditional "police state" experiences of cults is there when with Witnesses, sure, but there is just too much time Witnesses are out of that police state.
Some other aspects in the book make Witnesses sound cult like. They call their doctrine "The Truth" and while they take this more seriously than most, every religion does the same. Ultimately, I would say they are no more a cult than... Islam.
I will agree maybe with the term "high control group" maybe more than cult.