I personally know a handful of converts that came to Traditionalism (from other faiths) due to the Diamonds. All converts were men.
The Diamonds are a little nutty on some things, and I don't like their constant anathemas of heresy, but...in our overly feminized, wishy-washy, "maybe, sometimes" world, the Diamonds presentation of the Faith as "yes, yes and no, no" speaks to people, mostly men. It works. Can't argue with results.
Yes, and they've softened somewhat in recent times with the anathemas, but darn it if we don't need to hear it. There's a prevailing tendency in modern times, even among Trads, that heresy is "no big deal," since everything depends on "sincerity". Well, he probably "means well," so that's all that matters. It's the same subjectivist nonsense that has led to most modern errors, as well as the phenomenology that Bishop Williamson has expertly taught about, where ideas don't matter, are subjective, and that sincerity and meaning well and being "nithe" (as Bishop Williamson mockingly pronounces it) are all that count. Sometimes the Dimond Brothers do a service by calling a spade a spade and not performing some mealy-mouthed dance around it.
One need only look at the writings of the Fathers and the Councils, with all the anathemas they've hurled, to understand how seriously heresy was taken by them. Some of the language St. Jerome uses towards heretics would make anything we've seen posted by the Dimonds tame by comparison. It's important not to slide into a bitter zeal, but that can't be at the cost of going soft on heresy, since it destroys souls.