Augmented Reality (AR) has ever since made big promises in terms of improving maintenance in industry. However, long-term on-site assessments of AR maintenance worker support systems do not exist. In cooperation with three industrial companies we developed two such systems and conducted a 14-month evaluation period. The lessons we learned from the pitfalls we ran into during this assessment period provide valuable insights for researchers and practitioners alike who want to deploy AR maintenance worker support systems to the shop floor.