Dave,
The standard rear set up causes the car to understeer, as their is huge difference in roll centres / bump steer, so the standard rear actually makes the front push on (which if you study your crash footage, you can see this in action ).

The Grp A beams even up this disparity, which makes the car more neutral.

Franco,
This happened once on my car when the beam was first fitted, and Zoo paid for a full realignment and set up at my local alignment centre. I have not had any issues since.

Jakob,
As Paul says, the "strapped" version with motorsport rose joints would be essential in your pot-holed country . At present, this precludes the Bayjoo item, as it is not strengthened.