Many people naturally wonder about this question especially if they have never taken any Feldenkrais class or Functional Integration lessons before.
I do have slight hesitation to answer this question because I am a Feldenkrais practitioner. As a Feldenkrais practitioner, we try to shift people away from a goal oriented-mindset and shift them towards a self-directed learner because our society and culture tend to influence us to become more goal-oriented, which is not a bad thing. However, when we become fixated on achieving a goal, we tend to lose our awareness and attention from our own internal senses. And, as a result, we often overexert ourselves to a point we suffer both physically and emotionally. Setting expectations may cause you to look for and try to achieve those expectations. At that point, you've already lost your interest and curiosity about learning something new about you that may serve you well.
That being said, I will tell you what you should reasonably expect from ATM and/or FI. Both ATM and FI will provide you with opportunities to discover something new about you that will help you overcome your difficulties/challenges. That may be a new pattern (or new image) of movements, and that new pattern of movements (such as new way of breathing, walking, bending, running, swimming, singing, painting, dancing, etc) can have a profound effect on your life as it becomes integrated in your daily life. Anyone regardless of age, physical/mental conditions can learn and improve from their current state. There is no limit to learning and improvements. Even if you don't have any physical difficulties, you can improve yourself further and feel stronger, more agile, and younger than ever before. I can guarantee that you haven't reached your full potential yet. Why not move towards your full potential? ATM and FI can certainly help you with that. I don't know any other work besides the Feldenkrais Method that approaches from this perspective. Discovering possibilities and your full potential is definitely worth your time and is priceless if you ask me. If this work didn't have such a huge impact on my life, I would not have become a Feldenkrais practitioner in the first place. My answer may not satisfy you. I suggest you come to my class or FI session, or another practitioner's class in your area and immerse yourself in this sensory experience to decide whether it's worth your time and money.