Both Obi-Wan Kenobi and Rako Hardeen are voiced by James Arnold Taylor. Obi-Wan should not have needed to swallow a mechanical vocal modulator to impersonate Hardeen, simply change his accent. As accents are learned behaviors, he would need to speak with the Star Wars equivalent of an American accent, rather than an English one, when impersonating Hardeen anyway.
Cad Bane has been previously shown to require a special apparatus in order to breathe in an oxygenated atmosphere. The apparatus is missing in this story, yet he suffers no ill consequences.