Since Slattery's book expects you to take his word for quite a number of things, it was important for me to verify his accuracy.
Slattery asserts that Ellen White taught a shut door of mercy for all sinners after her first vision in January 1845 until about 1851 (pp. 15, 29). He states that immediately after Hiram Edson's "impression" about Jesus entering the Most Holy Place of the heavenly sanctuary, Sabbath-keeping Adventists first began to labor for the world (p. 15). However, Ellen White's first vision was in December 1844, after Hiram Edson's "impression" of October 23, 1844. If they started working for the world after October 23, 1844, there is no way Ellen White taught a shut door of mercy until 1851. It's hopelessly contradictory.
There are lots of less important mistakes, like Slattery saying that Adventists believe they will travel to heaven on a sea of glass (p. 21), when the sea of glass is what they stand on after they arrive in heaven, not what they travel on to get to heaven. Then there is his saying that William Miller started preaching in the 1820's (p. 14) when it was in 1831. He says that the Joseph Bates had Seventh Day Baptist ties, which is why he promoted the Sabbath among Adventists (p. 15). In reality, Rachel Oaks was the Seventh Day Baptist that told Methodist preacher Frederick Wheeler about the Sabbath. Perhaps Preble got the Sabbath concept from Oaks and Wheeler, Preble wrote an article on it, Bates read the article, and then Bates traveled to visit with Wheeler about it. Slattery leads the reader to think that S. S. Snow was off his rocker by 1844 (p. 14), but Snow didn't claim to be Elijah until after 1844. Slattery claims that Spectrum is an official Adventist journal (p. 7), but it never has been. All these facts are fairly well known and easily verifiable.
Slattery seems to contradict himself when he asserts that Jonah's prophecy against Nineveh can be implicitly conditional, but any condition for Ellen White's 1856 vision must be explicitly stated (p. 26).
If only the documentation were better. In order to prove that today's White Estate says that certain evidence is tenuous and cannot be validated (p. 5 n. 3), Slattery cites the 1919 Bible Conference minutes, a conference Willie White wasn't even at. He does this again on p. 38 n. 62 where he cites the same minutes as proof that a certain claim is still unverified. P. 53 n. 5 cites Signs of the Times 3-3-1888, but there was no issue with that date. P. 28 n. 20 cites an 1892 issue of Christianity Today for the opinions of Olson and Graybill, when Olson, the older of the two men, was born in 1920, and when Christianity Today didn't exist in 1892. P. 48 n. 5 cites the Adventist Review of Sept. 1868 for an alleged statement by James White about wine: No such journal by that title existed in 1868, Slattery doesn't say which of the four Sept. 1868 issues of the Review and Herald were intended, and an electronic search in all four issues for "wine" turned up no such statement by James White.
When read in their context, some of Slattery's quotations of Ellen White seem to give a different impression than what Slattery intended. Thus, I would highly recommend that any researcher who wishes to rely on Slattery first obtain the entire article or chapter his quotations come from, and see if Slattery's conclusions are really necessary. This is all the more necessary given the apparent inattentiveness to detail Slattery demonstrated in making the indisputable errors mentioned above.