Whether or not you should kill Yura, Hunter of Bloody Finger in Elden Ring depends really on what you want, both in the short-term and in the long-term. If you kill Yura, then you’ll instantly get his extremely long Nagakiba katana, without having to go through a long, difficult quest. However, you can get the Nagakiba katana without killing Yura, if you have the patience, skill, and persistence to do it.
After you first speak to Yura, Hunter of Bloody Fingers, you can go to the ravine northeast of Ahgreel Lake and help him to kill Bloody Hunter Nerijus and get the Reduvia, a powerful dagger. Next, you’ll have to kill the dragon in Ahgreel Lake, which is not easy at all, then help Yura in another battle, this time against a Bloody Finger Ravenmount Assassin. Finally, after you kill the invader at the Second Church of Marika in Altus Plateau, Yura will give you the Nagakiba katana. You’ll then have to survive a battle against Eleonora, which is tough but rewards you with another powerful weapon, Eleonora’s Poleblade.
If all of that sounds like too much trouble, then you should just kill Yura as soon as you first meet him, and then run off with his katana. However, if you want two other powerful weapons as well as the Nagakiba, then you should not kill him. You should make the effort to complete his questline instead.