Vallee is fantastic, and I would strongly recommend his books on UFOs as well. He's the kind of serious & careful researcher we need when it comes to studying complex problems that less serious people deny even exist, & his work stands out as reasonable and of excellent quality even compared to folks like Keel.
Like Keel, Vallee gets attacked by people who don't read him on two sides: by the people who are quite sure that UFOs are extraterrestrial visitors, and by the people who are equally quite sure that UFOs are the lies of con artists and the delusions of madmen. Neither explanation holds up to serious scrutiny.