What is the difference between lightgbm.LGBMModel and lightgbm.LGBMClassifier?
Glancing at the source (available from your link), it appears that LGBMModel is the parent class for LGBMClassifier (and Ranker and Regressor).  You should probably stick with the Classifier; it enforces proper loss functions, adds an array of data classes, translates the model's score into class probabilities and from there into predicted classes, etc.