Augustus Montague Summers was an Anglican priest and later convert to Roman Catholicism known primarily for his scholarly work on the English drama of the 17th century, as well as for his studies on witches, vampires, and werewolves, in all of which he professed to believe. He was responsible for the first English translation, published in 1928, of the notorious 15th-century witch hunter's manual, the Malleus Maleficarum.
This slender (24 pages, 145 copies) booklet is for completists only as the letters between Summers and Ogden only really concern the former's contracts with the publisher Kegan Paul for 'The History of Witchcraft'.
Sure, Summers touches upon some restoration plays and a other volumes he could write for them (a standalone book on Stigmata for example) but it's really pretty ephemeral stuff and should we really care about either at this point in time? Probably not; beyond wondering if the notes and/or typescript for the latter are part of the relocated stash of Summers material that surfaced in the States a few years ago. No doubt if it is, and it's good, it'll emerge in the fullness.
Don't pay silly money for it, unless you really ARE a completist...