[NickM]

Something not answered by the FAQ: when the battery starts to die, do you get some kind of a warning? If so, great. If not, I'd be worried that one day my battery would die without warning while I'm out of town and I'd be stuck without access to any of my cards.

Of course I could mitigate this by carrying my cards with me, but that kind of defeats the point, right?

I suppose I could also replace it after two years like they suggest in the FAQ. But at $100 a pop I'd like to get as much use as possible out of it. And from the usage numbers they cite for the 2-year estimate, it sounds like you could probably get well over 2 years of battery life in practice.

[OvidNaso]

It also appears to rely on your phone. It's certainly needs to be carried with an emergency card, but two cards as opposed to eight doesn't still preserves it's utility.

[g4m8i7]

It isn't that it relies on it, per se. You can set it to require authentication with your phone so it can disable itself if it's lost or stolen, but it works just fine without constant connection.