MFI Power Banks Necessary?

The MFI certification refers to the lightening port and cable that connects to the iPhone or iPad, not the device actually providing the power. Any battery pack that outputs standard USB power specifications (5 or 5.1 volts, and 1 to 2.1 amps) can be used with any MFI certified, or original Apple, USB-to-lightening cable to charge your device. It's that lightening connector and chip itself that manufacturers get certified, not the rest of their device.

I dont even remember the make of my little 1200mAh emergency battery in my briefcase but it works fine with my Apple iPhone cable and has worked fine with my iPhone 5, 6 and now 7.

The main thing would be to buy a reputable make (problems with cheap and unknown lithium batteries are common). And then it's a question of what capacity you want or need, and how much bulk and weight are you willing to cart around. Places like BestBuy, Staples, Offcie Depot, Target, etc usually have a good selection of backup battery packs if you want to get a feel for size and weight of various capacity cells.

If you want to recharge two iPhones and an iPad Air 2 from a single charge of a single pack, your going to need a large capacity battery (10,000-12,000mAh or larger) with at least one 2.1A output USB (for the iPad) which is going to be fairly hefty. There's no way to get that kind of capacity without the battery mass to contain it.

Anker products get great reviews and they seem to have a decent warranty and service. You're not likely to ever see an Anker product in an Apple Store though as that has never been Anker's approach. They don't seek out or market to major store brands. They do direct sales through Amazon and other marketplace hosts only (their founder was an ex-Google engineer so that may be where that thinking comes from?).

Mophie likely invested a ton of time, money and effort to get their products onto Apple Store shelves (for electronics, its prime real estate shelf space and reportedly extremely competitive to get on Apple's third party product radar). Does not mean their product is inherently better or worse. They just had a different marketing and distribution approach I'd say.

Until Saturday, I'd never bought my mophie product from Apple. However, I've been using them for years. I find them to be very high quality. I strongly believe one should never skimp on any power-related accessories. The potential for things going badly wrong is too great.

Check Amazon. Mophie updates their line every six months or so. You might be able to find "last year's model" on Amazon for a lower price. The ones I have are about four years old and not made anymore as they were replaced by sleeker, more powerful models. I figure, though, that if it can charge an iPhone and an iPad at the same time, it's powerful enough.

People have said good things about Anker here. Amazon might come in handy again as a place to read and compare reviews even if you don't buy there.

I've can't say I've ever heard anything bad about Anker. I have no experience with them and am personally skeptical about the price. I'd rather spend more up front than have to replace something more often. But in the end, only you can decide what makes sense to you.

And, yes, mophies are MFI certified.