Personally, I feel that undertaking a pupillage in the CPS is a dangerous move for a wannabe future practitioner. There's a real chance that you could lose your perspective, which is one of the elements that make the Bar so strong. To be able to prosecute successfully, objectively and efficiently surely one needs to have a deep understanding of how the defence operates? Vice versa, if you have a pure defence practice, it's entirely possible that you could lose objectivity and foresight in the long run. FWIW, I wish that criminal practitioners were required to prosecute and defend as much as possible!