The Disappointer is not useless... because you can remove the "terrible" attribute by enchanting it. (Damage, accuracy, fine, any of the first set of enchantments replaces an existing condition enchantment.)
I really wanted to use a pistol for my character concept, and so I stubbornly kept using this gun even though I missed all the time (on hard difficulty... yeah, okay, I did a lot of reloading) but just after leaving the first village I got enough components to give it a damage enchantment, and that boosted the damage from 65% to 115% and removed the accuracy penalty. Now it one-shots some of the enemies I meet at level 5 and really puts the hurt on the rest.
Where to find it: It's in concealed in one of the tents after you cross the bridge in the starter area. You may need some skill to find it, I'm not sure. (Edit: you need 1 rank in Mechanics.) You definitely need to be in stealth/detect mode.