I'm trying to manually reset values to factory default as listed in chapter 3, but I can't set the device friendly name to 'Multi-Tech SocketWireless' as shown. It is too long, over 15 characters, and contains a '-' which doesn't seem to be allowed.

This Bluetooth product ships from the factory with the Friendly Name set as "SocketWireless". When you do a factory reset back to defaults the two items that ARE NOT set back to default are the Name of Device (Friendly Name) and the PIN.

The Friendly Name can consist of 16 alphanumeric characters max.

Keep in mind that if you change the PIN from the "default" name, don't forget what the new PIN is set to. You will need to know what the PIN is if you decide to change it in the future. You CAN NOT reset the PIN back to default using the factory reset function. This is part of the security of the Bluetooth device.