Oro prob is after the Sharingan but wants it in its complete and most powerful form. goin back to the Zabuza saga, Kakashi says that his isn't complete and he can't use it perfectly. also Haku says something about bein supprised how Sasuke first uses the Sharingan in mid fight and it not being complete. some of the flash backs showin Itachi shows his eyes in Sharingan with 3 dots spinnin, while lookin at Kakashi's and Sasuke's only having 2 dots. Oro prob let Sasuke go so he could grow stronger and gain full access to the full powers and potential of the Sharingan naturally like any Uchiha could, cause he couldn't do it himself if it was a transplant like Kakashi's(imo).