I think they're fine as a secondary/roleplay weapon.
If you're playing an assassin/rogue/privateer/former magician/Zhat Vash defector/etc. they're fitting as a weapon with some traits to help like the S31 ground traits, and stuff improving/helping with flanking damage.
Comments
https://sto.gamepedia.com/Leck's_Throwing_Knives
https://www.reddit.com/r/sto/comments/l6z8z9/leck_throwing_knife/
All of it's attacks are classified as ranged though, so sadly it cannot be used to achieve the Melee Kill objective for Klingon Recruits.
Still, they're fun weapons.. worth playing around with. They don't really do it for me.. but I get why people like them.
If you're playing an assassin/rogue/privateer/former magician/Zhat Vash defector/etc. they're fitting as a weapon with some traits to help like the S31 ground traits, and stuff improving/helping with flanking damage.