Someone asked a Stans chap why they'd gone heavier, they basically said "Pretty much everyone who previously should have used a Flow should get an Arch Ex as it does the same job better. Except for the nutters, who should get a Flow Ex because they were always pushing their luck on the Flow anyway"
I can't honestly feel any difference between the Flow and Flow Ex in use (wore out a Flow on the 224 and fit an Ex to replace it). Found it harder to fit tubeless tyres to, just because of the width, but still not bad. Mind you my Flow lasted 3 years before it cracked with no other significant damage at all, while the Ex picked up a big enough flatspot on its second ride that it'll now not work tubeless. But that's maybe just bad luck, it did take a proper hit!