Opt is strikingly similar to another Blue card called Preordain. That sorcery allows you to Scry 2, which is certainly better as you get to dig two cards deep. However, Preordain typically can’t be cast at instant speed, being a sorcery. So while Preordain is banned in Modern, now having a card that’s functionally similar but also at instant speed means that Opt was certain to see Modern play.
Besides obviously being good in Standard in decks like W/U Control and Grixis Control, Opt was very quickly adopted by Modern Grixis Death’s Shadow decks, which were still looking for a good replacement for the recently banned Gitaxian Probe. Mono-Blue Tron and Grixis Delver have also been finding ways to adopt the instant. While Serum VIsions is a similar card that sees plenty of play in the format already, this is a good complement to that card.
If you happen to come across some old copies of Opt from Invasion, definitely hold onto them, since they are also legal in Modern (and Standard until October 2019). This is a very useful little card that will always find a home in some Modern decks.