I find it's not very broken except with certain cards (like Wishing Well). In games without it, and even without a point counter at all, I find I play the same way. This might not be true for other players, but I'm just giving my own anecdotal evidence.
I would play the same, basically, but it takes me extra effort to keep track of that stuff. Like, I KNOW that stuff, but it takes me effort to track it, which I of course do. Unless you're saying that it actually tells you what's left in the draw decks? In which case that really is broken and messed up. And yeah, it would have you playing a LOT differently. Or at least it would me.
And in all fairness, a point counter itself is "cheating." This DOES give you more information (a quick reference to how many duchies, total cards, unique cards, etc.) than a point counter, but I don't know that it's really that much worse of a crime than a point counter in itself.
Yup. And I agree, that the point counter itself is cheating, unless both players agree to it, in which case who cares? But more cheating is worse than less.