I was searching for a few newer book on Transylvania. One that caught my eye was a book called Transylvania and Hungary. The reason... not a good one.
I looked closer at it and noticed that the publisher is AuthorHouse, a vanity press. On amazon, looking into some details, it is ranked around 3 million in terms of sales. Still it probably will not be of any research value to most people.
Ont eh other hand in that same search a re-published book called Hungary and Transylvania might be of historical value since the book is pre-1923, which will be of interest to see what the people who had lost the First World War, and their views on the land which the ceded by the Paris Peace talks to: Romania and The future Check and Slovak Republics.
If you are not too careful about books, they might be something which is not great information, especially in a land where history is so and ever changing.