I run a 3x version of careful study. I feel confortable with it in most situations. Is a 1 cmc blue drop, improves your opening hand and is a discard outlet. In addition, and just in my experience, it is a spell that control players doesn't choose to counter because it is not such powerful as first spell. This let you put a dredger in yard very often. As a pro dredge card it is not comparable with breakthrough and i didn't have many opportunities of playing it with a dredger in yard. However, although it's powerful as pro dredger i always prefer colisseum threshold ability or, even better, breakthroygh. After all it is a good card to see in your hand with a land in play / hand. In my experience i didn't find a clear situation where i would have wished i had unmask instead careful study, except against combo decks...and so kind of pox i guess.
I found unmask amazing as postside card against combo decks. Yesterday, i could say that unmask gave me the necesary time to win against aluren discarding, in fact, aluren. I think that combo is the good match up for unmask sideboarding cutting studies. Beside against control decks could be useful since you can search for counter / hate cards, but for me this isn't a straight rule.
So...i think that if you see too much combo in your zone you should to run some copies of unmask in the main deck otherwise i prefer studies as main cards. However, all is about taste!!

