TOFO
Strongly suggest you disregard anything written on that website. I have over 4700 hours on the Firefly, instructing RAF, RN, AAC, & RBAF, and I do not believe the aircraft ever killed anyone. Poor training, or lack of, and incompetence can cause death in any airframe. As the old saying goes - even the family dog will bite if you kick him often enough!
With well over 6000 military Instructional hours I can state that the Firefly 260 was the best EFT trainer I ever flew, but like any other aircraft a flying accident can be your last.
Ray