TD wrote on 08/15/18 at 07:36:19:
I bought the books second hand. I have not enough money to buy more (new) books, alas. If I would buy one new book, which one should that be, you think? Ntirlis, Johnsen, Emms?
Okay, I'm buying dozens of books used every year, so I can understand that.
Which new book to buy depends heavily on your RL situation. If you don't need RL coverage, I would recommend Sverre Johnsen's book. It's the newest and it covers both 3. Bc4 Bc5 and 3. - Nf6.
I really like Bologan's non-RL book, but I believe it's already outdated in the slow Italian and the 2N main variation chapters.
I don't remember details about Lokander, not even if he covers the RL. I know though that I liked what I've seen. This book is a labour ofg love.
If you still need RL coverage and you like the Breyer, I would suggest Ntirlis. Bologan's second book covers the Breyer too, but one book should be enough. Ntirlis recommends the 2N though.
The quality of all these black repertoire books is high. Choosing one is a luxury problem. Maybe you want to download the sample chapters from the publishers' homepages and let your gut feeling decide.
It should be mentioned that IM Sielecki ( = ChessExplained) is working on an e4 e5 repertoire for black. It's scheduled for release on Chessable later this year. If he follows his old YouTube series he should recommend very solid variations close to Marin's books.
edit: Most, if not all, authors prefer to treat white's hyper-aggressive tries in a principled way. This means they're trying to refute them. Such a way of playing demands concrete knowledge. Often a second, calmer continuation is mentioned, but that's not always the case. There are openings like the Middle Gambit, in which white can force black into open combat with opposit side castling. There is no playing it safe in such a situation ...