Thinking back to middle school, I can say that I don’t regret my How To Draw Manga phase at all. During this phase, me and my pals would always get How To Draw Manga books. Some of them were questionable, others were pretty cool but rarely covered ground that a regular book on drawing wouldn’t have covered. But ultimately, it got us drawing. It kept me going too. I still, in fact, have one of those books by Ryo Toudo (it’s seriously a good and accessible tutorial book for inking with traditional materials!). Also I find it interesting how those books came out at a time where the anime and manga industries were already shifting styles, so these books were teaching stuff based on late 80s and mid 90s art styles to us in the early 2000s.
I’m not sure where I’m going with this other than I look back fondly to my artistic development which goes something like:
Triangle body/stick figures -> First copy of Shounen Jump released in the US -> Start copying that -> How To Draw Manga books were in vogue -> etc etc etc
I still want to keep improving, of course, but once in a while looking back for a little encouragement doesn’t hurt.