In section 2.3 between equation (3) and (4), the author mentioned "the maximum entropy estimation is guaranteed to be ... (b) the same as the maximum likelihood solution..."

So at this point, the MEMM is not different from HMM. Given HMM can also do exponential distribution, it seems that the MEMM is only new in "conditional" part.

Anyway this is a practical work. I am not critisizing its lack of theoretical construction, but its lack of mentioning of theoretical background.