ALG is not just an internal pollster: it is the Democratic internal pollster. It's the go-to pollster for the usually secret internal polling used by DNC, DSCC campaigns and even presidential campaigns. Obama's internal swing state pollster in 2008 and 2012 was ALG; they're the ones who gave the campaign the level of confidence they had in the final days and weeks.
Regardless of its 08/12 accuracy level, internal pollsters should always be viewed with skepticism. They are likely to configure their results to please their customers and to not care about accuracy.