lets not mix AV with STV, which was not on offer.

the study i read was quite categoric that AV would increase the chance of coalitions, for all that coalitions were becoming more likely due to a more plural voting pattern.
in doing so it would damage the utility of the manifesto mandate.
and it would lead to less radical policy due to the need to tailor policies to the expectations of potential coalition partners, and yes, this was the australian experience.