This question is asking for the reliability of a book, but I am wondering if questions asking for the reliability of something, a site, a book etc, is on topic here? I would right away guess that it is because questions on here asking for the reliability or grade of a hadith is on topic, but I just want to make sure.
Generally, the answer is "yes," it is okay to ask these kinds of questions. Islam is a religion of knowledge, and we live at a time with a lot of cultural practices and misconceptions, so it's important to at least know what kind of sources people are bringing.
At the same time, we have had cases in the past on this site where people use these kinds of questions to attack other beliefs. For example, we have had shi'a users making comments like "Aisha is not a reliable narrator" and sunni users making comments about shi'a hadith being "books of lies."
If you see this happening, please flag the comment or answer, and DV appropriately.