Not very widespread i think. Unless you regularly face strong titled players who made specific preparation for you, learning openings is 90% learning the ideas and 10% learning the concrete moves (unless you play really sharp and forcing lines, but even then the main lines appear rarely on the board between two amateurs, and quieter understanding-based lines subvariations will be commoner). And an engine opening book is of course rather useless in terms of teaching you the ideas.
Creating an engine opening book with the lines you already studied on a classical book and then using it to practice is certainly commoner and more sensible.
I'm writing a blog article and I'm interested in how many people read books vs don't read books.
I have seen posts here before where people said they never read books since they use the opening book for their engine to learn openings and I'm wondering how widespread that is.