I’m a fan of externals, and I own a fair number of them. Some things to keep in mind with this one (which I don’t own, but I’ve got similar ones):
(1) It will take forever and a day to fully charge. Take how long your smartphone takes to charge from empty and multiply that by a dozen or so. A long, long time. So, if you plan on taking this with you, don’t forget to check the charge long before you leave. Related: if you try charging this with a 1A/5W charger, it’ll take twice as long as with a 2A charger, so… choose the charger wisely.
(2) If this works for a week or so when you get it, it’ll probably work for a really long time. They tend to crap out quickly or take forever to fail. I’d not even consider the warranty, though, as a lot of these vendors are gone/renamed before warranties expire.
(3) Note that, although this has two ports, one is 1A and one is 2.1A, so the 1A will take larger to charge something… but, 1A ports tend to charge more efficiently, so, if you have the time, and your device will charge at 1A, go with the 1A port.
(4) This doesn’t have pass-through charging, which means you can’t charge it while it is charging something else. If you plan on taking this camping, no worries because you’ll have no outlets to charge it with, but if you’re travelling with it, I’d recommend a pass-through charger, but those cost more.
All in all, for the price, this is a decent but not great deal. Personally, I prefer pass-through chargers or, at least, chargers with more ports (or, if not pass-through and if not more ports, then smaller and more portable ones). But, if you’ll only be charging 1-2 devices and have time to charge this up first, go for it.
Edit: after a brief stint on Amazon, it seems like the Kmashi MP828 20000mAh is a much better deal - $10 less, nearly the same capacity, the same ports, and it includes a 5A charger to speed charging (but you can also charge via micro USB, like all the other externals).