FE2SLS is the authors' explicitly preferred estimator; among FE2SLS, the price-instrumented specification controls for measurement error in price || 'our preferred approach to estimate the rational habits model is based on the ﬁxed eﬀects two-stage least squares estimator (FE2SLS)' (p.13) and 'the FE2SLS estimator is our preferred estimation method. To control for potential endogeneity of electricity price, we also estimate the FE2SLS model by instrumenting the price as well as the lag and lead of consumption' (p.14-15)
Filippini, M., Hirl, B., & Masiero, G. (2018): "Habits and rational behaviour in residential electricity demand." Resource and Energy Economics, 52, 137–152.