A monthly $30 will soon grow more expensive than a few decent textbooks that cover the same material in greater depth.

One of Destroy All Software's primary value propositions (even included in the subtitle of the front page of destroyallsoftware.com) is terseness. My customers pay me more money because I produce small things. You can get quantity anywhere.

No I get that, and I enjoy your writing. It's certainly a valuable niche to occupy.

I just think people tend to underestimate the ROI on buying and working through a textbook.