Revised Dec. 2, 2016:To its credit, Logitech replaced my keyboard, whose battery door had broken on first use. It took several weeks, but the company acknowledged the delay and, to apologize, didn't ask me to go through the hassle of returning the original keyboard. (I had mailed the broken battery door with a note requesting replacement of that small part only.)The battery door is flimsy (slide one side first, then the other, to limit the force applied), but I've upped my rating to 4 stars because the keyboard is quite useful.Although the K780 supports Bluetooth, there are advantages to using Logitech "Unifying" USB receivers, one of which is included. First, a USB receiver is essential if your computer has an older Bluetooth chip. Bluetooth 4.0 is the minimum for "Bluetooth Smart", which this keyboard requires. Second, once you've paired the keyboard with a USB receiver, the keyboard will be available the moment you power-on the computer. This is handy for changing BIOS settings or pressing modifier keys, for example, to boot from a data DVD. Bluetooth drivers aren't loaded until much later -- so late that on some systems, you cannot type your Windows password from a Bluetooth keyboard!The K780 can be paired with three devices. Good computer stores sell, or can order, additional Unifying USB receivers. A cheap way to get them is to wait for a sale on Logitech wireless mice. (Look for the red Unifying star symbol on the package, because the cheapest models have single-purpose, non-Unifying, USB receivers.)To use the K780 with a computer that doesn't support Logitech's Unifying software (computers running older versions of Windows and MacOS, and computers running Linux, unless customized), plug a Unifying USB receiver into a computer that has the software, pair the keyboard and the receiver, unplug the receiver, and plug it in to the old computer. With Unifying, the keyboard (or mouse) remembers the identity of a specific USB receiver. Logitech's software is necessary for initial pairing, not for ongoing use.Initial Review:You wouldn't expect a keyboard with a $79.99 list price to break before first use, but that's what happened with my Logitech K780.Usually, a battery door has ridges, so that your fingers can slide it open easily. Logitech, however, opted for a smooth surface.On my K780, the plastic claws that held the battery door closed were tight. The tiny, smooth, rounded indentation made it difficult to generate enough force to slide the door. When I did get it open, the plastic claws snapped. The battery door no longer locks closed.It's also amusing that the instruction sheet inside the box was designed before the keyboard. It shows a door that slides toward the top, and straight off. The actual door slides the opposite way, with about 2 mm of travel before it has to be pulled out.I'm mailing the broken battery door to Logitech and will update this review if I receive a response. I doubt I will, as Logitech seems to have been reduced to a Chinese manufacturing operation with a skeletal North American sales and marketing presence. Make no mistake: despite the steep price, this is cheap, Made in China junk.(Before you ask why I opened the door right away when batteries are included, I always install those horribly expensive long-life batteries in my wireless keyboards and mice. It's worth it to avoid having to re-pair devices so often. The K780 is, after all, a 3-device keyboard. Before you point out that the door on your K780 slides easily, plastic molding is not an exact science, and tolerances vary from one unit to the next.)