Yes, you can use it with Arduino.
Also, the USB connection is pass through, so you can communicate with Arduino while PiUPS is connected to your computer. You then just disconnect it from your computer and Arduino will continue running.
Also, the mounting kit we have designed will work with Arduino.
Yes! PiUPS will work with Beaglebone also.
The USB connections on PiUPS are pass through, so that when Beaglebone is connected through PiUPS, it will enumerate on your computer and you can connect to it as usual.
You can then just unplug it from your computer and take it anywhere. Also, the mounting kit we have designed will work with Beaglebone.
At the moment PiUPS only supports NiMH rechargeable batteries, but we are developing support for other chemistries for future (through a software update to PiUPS).
Please read Update #1 for more information.