With the latest taboo (summer 2021), telescopic sight goes from an extremely situational card that you have to build around… To a situational card you have to build around. It's still a 3xp card you can’t use on others, and it can only trigger off a half dozen cards in guardian, and many of those start at three XP. (You can use it on Becky, the Thompson or the Winchester, but those are slim pickings.)
At its best, this is marksman on tap. Campaigns like Dunwich love spawning aloof enemies and putting them nearby, or regular enemies ahead of you. Same thing with the Innsmouth Conspiracy, although a hiding space or two will make this much more viable. (Oddly, you can use your telescopic scope while driving at 50 mph.)
But it’s a puzzle piece, and if you bring this, you’ll probably want extra ammo, enchant weapon for more damage, blessed ammunition, and well-maintained. And without two or three other players, you simply won’t have the enemy density to make this worthwhile compared to get over here or the riot whistle. Pair with Trish, Rita or Winnie for easier targets and less misfiring.