They might be worth a try. To clarify their capacity rating, on the picture of the batteries you can see they say 2500 mWh (milliWatt*hours), but the standard way of reporting it for NiMH is in mAh (milliAmp*hours). If you want to know (in joules) the energy storage capacity, you can't compare the two straight up. For example, I've got some 2600 mAh NiMH's in my flash right now.
2.5 W*hrs = 9000 J
2.6 A*hrs * 1.2 V = ~11000 J
so the NiMH actually edges out the NiZn batteries. It's a pity engadget didn't test a set of high-capacity NiMH's, too.
As far as using them for flash, to me it seems like the capacity isn't probably as important as the internal resistance of the batteries (the quicker you pull charge out of them, the more they resist and heat up). If the NiZn have better flash recycle times and don't heat the unit up as much while doing it, then that could make it worth it to switch. I wish they'd been more thorough.
Also, someday soon I'll wager we'll see these batteries being used in flashes and not just in autos.