Thirty posts, each one asking whether a marketing channel actually works. Henry Brady wrote short verdict pieces: is article marketing dead, does video marketing earn the time it costs you, where do you even start with a website when nothing is built yet.
The format stays consistent and that is exactly what makes it useful. Name the channel, say plainly what it is for, then say whether it still pays. Personal development gets the same treatment as search optimisation, on the reasonable grounds that both are things people buy into without ever checking.
There are product reviews mixed in, including affiliate offers he promoted himself, so read those as the pitches they plainly are. The channel posts are the substance and they hold up rather better.
Worth your time if you are deciding where to put your effort and want a short answer from somebody who tried several things, rather than a long answer from somebody selling one.