What are the top places in Burundi to get the best currency exchange rates, and how do reliable options such as local forex bureaus and major banks compare in terms of rates, fees, and service quality? Additionally, how do different locations like airports, hotels, and city centers impact the exchange rates offered to customers? Furthermore, what key factors such as exchange margins, hidden charges, and real-time currency rates should be considered to ensure the most favorable currency exchange experience in Burundi?