I've had these long enough now to feel confident in giving them a review, and so far? They're perfect sketchbooks. The paper feels good with my pencils, and the 3 sizes are appreciated. For the price you get an incredible amount of paper across the 3 books, and my most-used so far has been the smallest one.
The slip covers are nice, though I think unnecessary, and often times when I'm drawing I simply take them off as they otherwise get in the way, but when I'm not using the books I leave them on to protect the exposed spine. They're also fun to doodle on if you have a white pen or pencil. I have yet to tear through any piece of paper using a 0.7mm lead, and my only real issue has been a slight bleeding when using my inking pens, which is barely noticeable and didn't affect the other side of the page.
Overall, highly recommended. I haven't had any issues with the books falling apart, and I certainly don't see it happening anytime soon, given the fact that the binding is actual twine from the looks of it.