Two bags, two very different jobs. Here's the honest breakdown.
If you're driving somewhere: the Overnight Bag wins. It's bigger, it's built for road trips and caravan life, and it handles the actual logistics of car travel better than a hard case ever will. Hard cases are rigid whether you need them to be or not; this one folds flat and squishes into whatever odd-shaped gap is left in the boot once everyone else has packed. When it's not being dragged around Australia, it flattens down and works as bedding or off-season clothes storage, so it's not just sitting empty between trips.
If you're flying: the Zip Medium Tote is the better call, because it was actually designed for it. It has a long shoulder strap for getting through airports without your arm going numb, and a luggage strap that slips over your suitcase's telescopic handle so you're pushing one thing, not carrying two. The part that matters most for carry-on travellers: it weighs 270 grams. On a 7kg allowance, that's barely a rounding error, which means the weight budget goes to your actual stuff instead of the bag carrying it.
Different trips, different bags. That's really the whole story.