It looks like the big advantage of it is that you can store it practically forever without self-discharge. The other advantage is that you can carry more than one hydrogen cartridge for a minimal increase in weight and bulk. The recharging unit ("hydrolyser") costs $250. The cartridges, at $15 each or 4 for $50, aren't that expensive and are supposedly good for 1000 refills.

I haven't seen specific power-density figures but "iPad-recharging caps out at about 1.5 times per fully-juiced cell." That's about 12,000 mAh. Size is 5.3 x 2.9 x 1.3" and weight is 8.5 oz with one hydrogen core. Compare that to the largest of my collection of portable LiPo battery chargers at 4.8 x 3.1 x .9", 13 oz, and 18,000 mAh. In other words, the Brunton unit is lighter but bulkier and more expensive to operate.

My needs for portable recharging revolve around air travel, power outages, day hikes and the occasional night or two in the boonies. For that, a LiPo battery makes more sense to me. Hard core backpackers and adventurers would probably be better off with the Brunton unit.