The right device depends on the job
All of this made me realize that my decision would rest more on functionality than on form factor and it made me really consider the use cases for each device compared to each other and compared to my iPad mini or an iPad Air.
Since I use both my iPhone and iPad as much for work than personal use, I really needed to sit down and compare Apple's new smartphone, phablet, and tablet from a business user's perspective. That's when I realized a couple important things.
First, the iPhone 6 Plus does offer behavior more like that of a micro-iPad than an iPhone, at least where Apple or third-party developers have made the effort to create apps specific to the device. This means that in some contexts, it will likely be capable of replacing an iPad (or an iPad mini), but that won't universally be true. In addition to putting my iPhone on my sketched outlines, I also put my iPad mini next to them. While the size difference between an iPhone 6 Plus and iPhone 6 (or iPhone 5/5s) is minor, the difference between it and iPad mini felt enormous. (It's worth remembering that manufacturers measure screens diagonally, which doesn't always capture the real world feel in the size differences between them.)
So how to choose?
Who needs an iPad. Although I haven't used an iPhone 6 Plus, it was obvious to me that some tasks common on iPad weren't going to be particularly suited to it. For moderate to heavy image editing and or anything more than light editing of Office documents, particularly large spreadsheets, the iPad is still the way to go. Even reading an entire ebook on it doesn't seem quite so appealing, though I've read ebooks on both sizes of iPad and an iPhone 3G's 3.5" screen and it is doable.
Who's best suited for an iPhone 6 Plus. At the same time, for someone that spends a lot of time collaborating and messaging, the iPhone 6 Plus is more than capable, and apps that use that extra screen real estate the way Apple has will provide a much better mobile work experience than the iPhone 6. Reviewing documents, PDFs, presentations, or video are also great business matches for the iPhone 6 Plus. For managers — project managers in particular — this is a very good choice of device. It's also a good fit if you typically wear a suit or jacket because the dimensions are a much better for an inside jacket pocket than a pants pocket.
Who might want to stick with a regular iPhone. If you're someone whose job revolves around much lighter mobile needs — phone calls, the occasional text, and brief mobile email responses — the added functionality may not amount to a better, easier, or more efficient experience. In that case, your personal preference for size may be the best guide that you have in making this decision.
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