I think that Landmark peaked in the US during the 80s-90s. The last I heard, it was growing the fastest in India and Israel. Werner Erhard did Scientology before starting est, and they never forgave him for recycling some of their stuff. And it's arguable that they were behind efforts to demonize est/Landmark, and paint it as a cult.

I do recommend it. But it's crucial to keep in mind that sharing your experience of the work, and encouraging others to participate, is an integral part of it. It's true that relationships of all sorts work better with people who have done the work. So there's some self-interest in sharing.

The courses themselves generally run from Friday evening through Sunday evening. About 12 hours per day, with breaks for lunch and dinner. Back in the day, they'd run a lot later, basically until everyone got the day's distinctions. But that's mellowed since the 90s.

For example, homework assignments involve sharing with family and coworkers, and inviting them to an evening session the following Friday. At the evening session aka graduation, guests spend some time with the main group, and then go to small introduction sessions.