The g403 isn't quite as ergonomic as the ec1-a and the weight difference through me off a bit after making the switch, even with the weight in. With the braided cord and extra weight the g403 is still lighter, the sensor is amazing and the buttons are honestly incredible. I didn't know how much of a difference it would make but holy shit, it's like going from a rubber dome to mechanical keyboard. The mouse wheel feels like the steps aren't quite as defined but it still feels better somehow.
That said, I loved the shit out of my ec1-a (non-benq) and only switched because the mouse wheel started fucking up and I wanted an excuse to buy a new mouse. The ec1-a is a bit longer, at least it feels that way, so you can palm grip it a lot more naturally than the g403.