I bought these about a month and a half ago under the same premise.. I actually can't say enough good things about them. I'd say they singlehandedly got me back into trying to play again (and better) to be honest. I was someone who noodled quite a bit (on the computer/online etc) but hadn't really formally gone through any sort of training and quite honestly found most of the english books really quite haphazard in their teaching style (going from way too easy to really impossible to follow in a short breath, or just really simply a list of concepts without linking them all together, in ways they show up in games). These books are clearly coming from the point of view of thinking carefully about pedagogy and further are clearly adapted from real (korean) course books. I actually find the fact that they are written for children one of their greatest strengths, because they are super systematic and super thorough, with a tons of problems for each basic concept.
They bring the basic idea behind how we would teach say math or science to kids to teaching go. Each book is divided into a simple basic concept (which are themselves split into categories like thinking power, judgement ability, spatial sense, reading ability, memory etc), a few examples and then say 15 problems around that concept. Just as in learning math in school, by the time you finished the last problem, you will have the idea down pat. Further each concept is interspersed with a series of reviews from previous books/sections and some really clever ways to get you to think about move types. An example of this is, is there are sections interspersed called opening moves where you play moves, read out the type of the move and repeat. Initially i thought this was a bit needless, but the 11th or so time you do this, you start thinking of stone flow in the way those plays are read out. Lastly there are 3 20 problem quizzes at the end of each book for review, which are useful to verify that you have learned each concept.
I agree with the slow knowledge adoption but its really one of its strengths.. and honestly you can read it at your own speed,. So for example I'm now somewhere in book 8 after about 3 weeks or so. While most of that was review (even now) I definitely got something out of reading them from (mostly an appreciation for how sloppy I am

). Its gotten me to do basic things much more methodically in a manner I wasn't really doing before (counting, reading out, knowing where / when to cut and connect and when not to, in ways I thought I knew but quite honestly did not.)
With all that said the one negative thing is there are mistakes in their answer sections in pretty much every book. These have all been really obvious though, but they really should be fixed.
The other thing I should add is for whatever reason books 11-15 (the jump ones) actually don't have a PDF answer book available but is being sold separately. YMimports (where I ordered these books from as well) doesn't have the answer book and aren't getting new ones for 2-3 months. I didn't realize this when I ordered them from ymimports, and now I am trying to figure out how to order the answer book directly from korea.
-regards
-avi