It is reasonably easy to shield from electric fields as long as the field strength isn't too high. But if the unit isn't allowed to have a conducting box, then you get a lot of costs for having an internal shield box.

It is way harder to shield magnetic fields. If your unit is sitting on a lamp post, and a lightning strike sends 30kA down through a metal pipe directly under the unit, then you really have quite nice magnetic fields to consider. And besides the need for mixing of layered Fe and Cu to try to handle the magnetic field, you also have the problem that a traditional unit has some way to receive power and possibly antenna, and signal data.

So yes, shielding helps, but normally can't completely solve the problems.