Pros
UNDP has been very good reputation across world. You will understand how govt. and UN organisation are working together for the people on different causes. Knowledgeable and good human being works in UN system. They never compromise with security of their staffs. It has women pro system.
Cons
Salary never increases annually in UNDP. You will get 1% - 3% bonus against your annual performance. You would not be promoted to upper position as their system not allowed it. You would crack that job though fresh selection process. However, It is right that UN will prefer their people as he understands their system and process. Those are working remotely never feels that they are similar to Delhi HQ team. UN system and process are slow and complex.