Grazing muzzles

What experience is there with Grazing muzzles
There are a number of variants from the plastic mesh like the greenguard
to 
the fabric with the hole in the bottom.
The latter looks hard for a pone to get ANYTHING at all in long meadow
grass 
but is it just a matter of training?
Advice would be appreciated.

-- 
regards
Jill Bowis

Domestic Poultry and Waterfowl Solutions
Herbaceous; Herb and Alpine Nursery
Seasonal Farm Food
http://www.kintaline.co.uk