Bet Angel is optimised to give the best performance when connecting to Betfair. But your bandwith really depends on the types of markets you trade, how many bets you place and at what rate you refresh those markets. A tennis "match odds" market only retrieves odds for two players, a golf tournament 40-60 players or more. This is the first impact you will have on your bandwidth. The second impact is how quickly your refresh the market. If you refresh once a second, this is a low impact refresh speed, but if you refresh at 200ms you are then pulling five times as much information from Betfair.
The easiest way to measure you bandwidth usage is to run usage monitoring software such as BitMeter2 which is available at this URL: