I think one of the things that really brings Sakon and Ukon down is that, compared to the other sound 4, they don't really have any unique character defining traits, which really makes them forgettable, even with their unique joined twins kekkei genkai.
>Jirobo - the fatass who's a glutton
>Kidomaru - gamer with a 200 IQ
>Tayuya - plays a musical instrument and is really aggressive for a female character
>Sakon/Ukon - Uh, they're violent and they want to kill their opponents (something which is extremely common for Naruto villains)