Applets that try to access IOBluetoothDevice tend to crash with
This app has crashed because it attempted to access privacy-sensitive data without a usage description. The app’s Info.plist must contain an NSBluetoothAlwaysUsageDescription key with a string value explaining to the user how the app uses this data.
I created the necessary key with Xcode, and now the applet asks for Bluetooth access as needed instead of crashing. But it would be useful to handle that sort of thing inside SD, whether you want to add more keys to the Bundle & Export Settings or just give us a way to ruin modify the plist directly … maybe with a scary “use at your own risk” warning. 
Also, SD crashed when running a script with the same code (cribbed from Shane’s post on MacScripter), so I had to add SD to the Bluetooth access list in System Settings by hand.