1200W are the highest power ones. I'm gonna guess that when they say "common microwave", they mean 800-1000W, which is what food packaging uses (and what people actually have), so that cartridge is likely 3kWh. It doesn't include a fuel cell, so you can't just plug it in like a battery.

So it's 5.5kg, plus a fuel cell vs 15kg for a battery that doesn't need extra parts to produce electricity. Also, can't recharge on common infrastructure, cost is not mentioned, etc. Overall a slight improvement that's practically useless. That's hydrogen in a nutshell for you.