Anker specifically states that the 24W charger is not compatible withdevices. A bit of research reveals a well-known quirk of Galaxy Tab devices' hardware and software that prevents the tablets from charging with non-Samsung chargers.
As a cross-platform tester, who often juggles an iPhone and an Android phone for work, and as an Android user who's surrounded by a circle of iPhone-toting friends, I found the Anker 24W charger's ability to offer charging for both worlds to be extremely useful.
If you're not a cross-platform user, you can also charge two Android or Apple devices at the same time using the Anker 24W charger, but there is a potential catch. A device that finds itself plugged into the "incompatible" outlet may choose to recognize the charger as a computer's USB port, not a fast-charger, and revert to the slowest 0.5A rate of charging.
This is sort of the 24W charger's Achilles' heel: by choosing to appeal to both Apple and Android users with one device rather than two separate products, it's possible that it's not really perfect for devoted users of either platform. If you want to charge two iPhones at the same time, you've got some decisions to make about which device will get the fast-charging and which will have to trickle-charge. I suppose you could swap back and forth. If you're charging an iPad and an iPhone, you don't really have a choice but to trickle-charge the phone, as the iPad won't charge from the other port.
Android users have it a bit easier, as many Android devices will actually still charge reasonably quickly when used with the Apple-specific port.
However, if you're only carrying around one device, having the extra powered USB charging port around for a friend or family member to use in a pinch is nice, whether it is or isn't the optimal charging rate for the other device. Any port in a storm, so the saying goes.
Pricing and availability
The MSRP for Anker's 24W car charger is $35.99, which is about double or triple what I think most users are comfortable spending on a third-party car charger that doesn't include a Micro-USB or Lightning cable. However, I was able to find the charger offered for just $11.99 on Amazon at the time of this review. That's a much more reasonable, even generous price, even if you only plan on taking advantage of one of the Anker's two fast-charging ports. Look for a deal like this and you won't be disappointed.