[glang]

The big disadvantage of using a flow meter is that it measures just one carb/throttle body at a time and as it works by creating a slight restriction affects the tickover. So in swopping it between the measurements youve introduced a small variable that creates inaccuracy which on a car is insignificant but on a bike more important.
You can balance the carbs very accurately without expenditure by using a home made manometer. You just need a long length of plastic tube and some water....