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Pro Full Windows software
Unlike the Surface RT and Surface 2, the Surface 3 runs full Windows 10 software. With the optional keyboard accessory, this tablet can function as a full laptop (keep in mind it has fairly low end specs)
Pro Optional keyboard accessory
The keyboard ($130) doubles as a screen protector when not in use, and magnetically attaches to the bottom of the Surface. It's thin, so key travel is shallow, but it's a very capable keyboard. It features 5 levels of backlight, as well as a (rather small, but very high quality) trackpad. It connects directly to the Surface, so there'd no need to charge the keyboard and you don't need to worry about bluetooth.
The Surface 3 has a kickstand on the back of the tablet so that it can hold itself upright. It has 3 positions - one upright (almost vertical), one at almost a 45 degree angle, and one fairly close to flat (this one is useful for drawing or typing if you don't have the keyboard).
Pro Optional Pen accessory
The Surface 3 (when coupled with the $50 pen) can register 256 levels of pressure sensitivity, and also has Palm Block technology. It makes for a good experience when drawing diagrams, sketching or even just doodling. Clicking the button on top of the pen opens OneNote - Microsoft's note taking application.
At just 267x187x8.7mm (10.5x7.4x3.4") and weighing 622g (1.37lbs), this is a portable machine. Some other tablets are a bit thinner and lighter, but the kickstand really helps you comfortably use it anywhere (you could set it up in the kitchen for a recipe instead of laying it down flat, or rest it on your chest while laying down in bed instead of holding it up).
Con Small app store
The Surface 3 is almost better as a laptop than tablet because it has so few touch-enabled apps. It uses the Windows Store to access its games, so it has the same collection available as desktops and laptops.
The screen is very susceptible to being damaged. Here's where its generally beneficial light weight can be a downside. It requires as much protection/care as a tablet does -- it is not as sturdy as a laptop. The back cover will scratch fairly easily if dragged along a table as well.
Con Very slow to charge
The Surface 3 uses micro USB to charge which is nice because cables are plentiful, but charging from empty to full takes about 6 hours.