TL:DR Grab Flashlight if your is low or mediocre, it's outright amazing solo but looses it's luster progressively with player count, it picks up again on hard and expert as a means to cheat low difficulty locations.
The ubiquitous Flashlight is at this point a legacy card, its one of the more decent cards in the core set, but it is a little specific.
When a difficulty test is (0) it's automatically passed regardless of what token you reveal (except if you get ), this means that a Flashlight outright wrecks easy locations, this is a good means for 1, 2 and 3 characters to help in the clue game. It has combo potential with some skills, netting you guaranteed hits with Double or Nothing, Deduction, Resourceful and so on.
In higher difficulty this ability to cheat some locations is even better, those -5's and -6's really don't impact you when everything but succeeds.
.
Flashlight isn't a must have though, when player count grows and the clues start getting placed in bulk Flashlight just doesn't cut it anymore. A solo character who is bad at clues might be able to finish 2 easy locations with just 1 flashlight, and cheat the hard locations with other tricks, in 3-player it'd only get you through one location! Of course if the full team is doing their thing then beating one location isn't terrible rate, but specialization is the name of the game in multiplayer and a fighter spending 4 actions, 2 resources and the card slot to beat a 1 or 2 difficulty location isn't the best use of his time at all.
That said, Flashlight isn't bad for flex characters in multiplayer, dudes like Roland Banks who can pretty even-handedly do clues and combat, Wendy Adams until she gets Lockpicks, Sefina Rousseau as a means to conserve Rite of Seeking charges.
It's a fine card, but it's definitely better on higher difficulties and lower player counts (ideally: Solo).