I have them both, and I value them both in their own way.
TBMM is more specifically targeting low back pain, and it is an integrated approach which ties the client into the process of homework in a very smart way. It is more specific and has a recommended sequential approach which works very well.
NASM CES is an extension to the NASM CPT approach using their OPT model which you, as an ACSM certified trainer, are probably not familiar with.
In your case, I would lean towards TBMM. I found it very practical, and Justin is a VERY HELPFUL person. You can contact me in person, if you like more information.