I had the Safe N Sound Meridian AHR for both my babies and thought it was great - seemed nice and comfy for them, great for rear facing and then still has a long life once you eventually turn it to forward facing - I think it goes to 18kgs but don't quote me on that? It is all one "thing" though so yes, you would need one for each car.

We just got a letter from the RAC (not sure what your Vic equivalent is?) that had the recent car seat results from capsules through to boosters - it was done in conjunction with the other States' RAC equivalent. Google RAC and then search for child car restraints and the links are at the bottom of the page. HTH