The dongles are like the nano dongles Logitech uses for its wireless mice. They will only pair with one device (although Logitech now offers nano dongles that will pair with multiple devices, i.e., mouse + keyboard). Bluetooth should do the same, but I haven’t received my Bluetooth module yet so I can’t test that.
You should be aware that there is a signed driver available now (looks like WinChipAhead recompiled their driver and signed it). You can get it for free here. The driver should work with Yosemite, and I’m using it with El Capitan. You may need to uninstall any other USB drivers and there is a link to a page in this thread that discusses that process.
UPDATE:
I received my Makeblock Bluetooth module for the mBot today. I was able to connect to the Makeblock app on my iPhone, but no luck with my Macbook or iMac. I tried using a 3rd party Bluetooth dongle in both, and was still unable to stay paired (the device would pair and then immediately disconnect). There was a pop-up dialog with a pairing code, but I’m not sure if that’s an Apple security thing or not. Still investigating to see what’s up although El Capitan has a lot of bugs that Apple is still fixing especially with regard to Bluetooth and WiFi.
Regardless, my recommendation is that if you are planning to use mBots in a large scale that you go with the WiFi versions if you are planning on having the kids run programs through mBlock. Bluetooth does not appear to be reliable at this time in El Capitan (OS X 10.11.3).