Yes there are several differences.
ACSM is an NCCA accredited credential.
AAHFRP is not.
ACSM CES scope of practice is different than the AAHFRP MES.
AAHFRP does not prepare one to work with cardiac or pulmonary
The ACSM CES is a clinical credential AAHFRP is not.
By the way, I hold the AAHFRP MES and am just about to complete the AAHFRP MEPD credential and it has only been instrumental to my professional growth. I also hold ACSM RCEP credential.
I have no regrets about taking the MES and MEPD courses. It has only helped me become a more critical thinker in terms of program assessment and design.
Hope this helps.