all nutrition certifications will give you great detailed information to share with clients but the fine line of scope of practice still remains. Unless you become an RD, you will be limited to how specific you can be with your clients.
I have the NASM FNS certification and learned A LOT. I feel that I can offer plenty of advice and still stay within my scope of practice.
I personally found the Behavior Change certification more relevant. I find that clients do not necessarily lack knowledge about food but don’t have the strategies to apply that knowledge.