This device will ensure only 12 volts goes to the MOFI router.
The reason you might need this device is if you plan to use this full time in a vehicle, boat, or anything that might have unstable voltage.
For example, in a vehicle, when you start it, it can push very high voltage for a fraction of a second that can damage the unit.
When using this voltage limiter, it will only allow 12 volts to be sent and therefor protecting it from any spikes.39.99
This can be used with the build in fuse or you can just cut that wire with the fuse and connect directly to a 12-36 volts input and put the other end (black wire) to ground.