Yeah, I had one of my old Japanese profs recommend these books as well. I picked them up a couple of months ago, but I haven't had a lot of time to play with them yet.

The beginner book is a good review book if you're coming back to Japanese, or if you feel a little rusty, or if you just want extra practice, or if the textbook you're using just stinks at explaining a certain point. (Although it can be pretty vague as well.) It's only 1400 yen, so it's not a bank-breaker, but it's a bit short at only 129 pages. Answer key in the back.

There are lots of really good fill-in-the-blank and choose a/b exercises, if you want to add those into an SRS. And the explanations are given in Japanese, English, Korean, and Chinese, so if you want to, you can try to ignore the English and read the Japanese. (Prepare for the next level.)

I wouldn't look to it to "crack the mysteries of Japanese," but it's a good book for drills.

ISBN: 978-4-88319-328-8

The intermediate level book is a lot denser, being an intermediate level book. ~295 pages, and 2000 yen. Answers are also in the back. Less English, but just enough to give you an idea of what's going on. Lots of exercises to practice, with answers in the answer key in the back.

The way it's organized, I would say it's NOT a replacement for an intermediate Japanese text. It's breaks things down by subject categories, so point #1 covers particles of all kinds, point #2 covers topicalization (things like というものは、に限って、といったら、...) it goes over a lot of stuff, actually. There's a lot devoted to phrases used like particles-- 3 chapters. It's pretty dense in comparison.

ISBN: 978-4-88319-457-5