Authors explicitly prefer the ML estimates: 'ML is preferred to GMM-AB based on this generalized R-squared criterion. Moreover, the ML-based estimates are generally more statistically significant, indicating that it may be a more efficient approach' || 'ML is preferred to GMM-AB based on this generalized R-squared criterion.' (p.597, Table 4 note)
Cialani, C., & Mortazavi, R. (2018): "Household and industrial electricity demand in Europe." Energy Policy, 122, 592–600.