People tend to have several devices -- a laptop, a tablet and a phone for starters -- which is why Logitech keeps putting out "multi-device" Bluetooth keyboards. The company's newest model, the K380, which I'm using to type this, costs $40, £35 or AU$70 and is one of the better wireless keyboard bargains out there.
The first thing you notice about it is that that keyboard has a little bit of heft to it, which makes it suitable to use with a desktop computer (I'm typing on an Apple iMac), though it's still light enough to be travel friendly.
You can set it up to pair with three different devices and press one of the numbered "Easy-Switch" buttons in the top left corner of the keyboard to toggle between them.
The keyboard can distinguish between say, a Mac and a Windows machine -- I have a few of those, too -- and map keys to supported functions and shortcuts, which is pretty nifty (the K380 also includes support for Chrome OS, Android and iOS devices, as well as Apple TV).
I liked the feel of the keys and they're spread out enough to keep mistypes down to a minimum. After using the keyboard for a couple of hours I thought it was only a slight step down from Apple's $69 Wireless Keyboard, which is only designed to be used with Macs.
Aside from the multi-device support, the other selling point of the K380 is that Logitech says that the two included AAA batteries will power the keyboard for two years. I'm not sure how much use that's based on, but even if it did half that it would be good.
Logitech also makes the $50 K480 multi-device Bluetooth keyboard. That model is wider and includes an integrated slot that holds phones and tablets (it also uses two AAA batteries). I personally prefer this model because the tablets I use tend to have cases on them that convert into stands, so I don't need the slot.
As part of the new keyboard launch, Logitech also trotted out a new compact, portable Bluetooth mouse, the M535. Available in black or blue, the mouse works on just about any surface "thanks to a laser-grade optical sensor." It's pretty straightforward looking but has textured rubber grips, a tilt wheel, and can last up to 10 months on one AA battery. It's also priced at $40, £35 and AU$70 and is designed to be paired with the K380 keyboard, which comes in grey or blue.
The K380 Multi-Device Bluetooth Keyboard is expected to be available worldwide in September while the M535 Bluetooth Mouse is due to arrive in Asia, Australia, Canada, Europe, New Zealand and the US in September.