To be clear: the linked database is for Mayflower Fifth Generation Descendants, 1700 - 1880. It is, indeed, based on the Silver Books (actually it's indexed images of the pages from the books.) The database does NOT cover the entire series - just the fifth generation books.
The database is an excellent reference for research, as the profiles include a list of references. As with any published genealogy, verify the information presented, either independently, or via the references provided. Some references are merely previously published (unsourced) genealogies; other references are published vital records, etc. The general quality of the research is similar to the better proflies here on wikitree.
EDIT: The series DOES have a few inconsistencies in the references. E.g., a couple of references for birth dates/places do not have the data cited. I haven't found conflicting information, but I could not find a record for information as cited.