I wear a Leatt.
It limits the range of head movement somewhat (as designed)
Not a problem on the trail where I can hear a faster rider approach from behind .
On multilane the restriction is enough to prevent effective head checks when lane changing.
If I have to ride the slab to get where I want I'll leave the Leatt at home - sure do miss it on the trail
If the Earth is flat why are my tyres round?