Apparently the pseudonym was chosen to protect his legal career from being tainted by public knowledge of his interst in conjuring etc. In his 1918 book, LATEST MAGIC, which bears both his pseudonym and real name on the title page and frontispiece, he writes: "A final word on a personal matter. Had I been a prophet, as well as magician, when I first began to write on conjuring, I should have chosen a different pen-name. In the light of later events, my selection was unfortunate. My identity has long been an open secret, but as I cannot flatter myself that it is unversally known, I take this opportunity to assure all whom it may concern that I am British to the backbone."
He did occassionally give charity performances (at least one program is preserved, a benefit performance for Professor Charlier, the mysterious cardman who tutored Hoffmann and others. Charlier also performed on this program, one of his few known public appearances). Much of Hoffmann's early work was translated from French (Ponsin, Robert-Houdin) and German sources. One of his most difficult to find works, and one of the few written under the name Angelo Lewis, is a book on the Indian Penal Code. Anyone out there have a copy? In addition to his great trilogy MODERN MAGIC, MORE MAGIC and LATER MAGIC, he wrote dozens of other books, PUZZLES OLD AND NEW being as seminal in the puzzle community apparently as MODERN MAGIC is in ours. His writing career superceded his legal one and he became a full time writer in his later years.