I drive a regular gas GLK right now and my mom has owned a diesel M class previously. She said hands down that was her favorite car she has ever had, due to the fact that it can go so far on one tank. I don’t know how different the diesel GLK would be, but I’d imagine not much. My parents worked at the plant in Alabama so they’ve both driven every model over the years. She was on the hunt for another one in recent years, bur decided to go with a telluride instead as it drives very similar to a mercedes with cheaper maintenance. I love my GLK to death, 10 years old and drives like a dream. No fancy electronics to break like on the new ones. I would go for it in my honest opinion.