I am considering purchasing this series. Would appreciate any comments from those that own it.
If you've got ACCS, you know the format.
It's great for answering, "What were the Reformers writing about this passage?". But a good modern commentary will be better at answering, "What does this passage mean/say?". That said, reformation-era commentaries tend to be both academic and pastoral, a mix that's very rare to find today.
One additional positive is that you do often get some very well-written, quotable comments on some passages, particularly from Luther and Calvin. One example at random (Luther on Romans 9:2),
"From this text it is very clear that love is found not only in sweetness and delight but also in the greatest sorrow and bitterness. Indeed it rejoices and delights in bitterness and sorrow, because it regards the misery and suffering of others as if it were its own. Thus Christ even in the final and worst hour of his suffering was aglow with his deepest love, indeed… it filled him with the greatest joy to suffer the greatest pain. For thus it is that “God is wonderful in his saints,” so that he causes them, at the very time they are suffering the greatest pains, also to experience the greatest joys."