As a former chef ( now pottery nut and teacher) I found this whole
subject very interesting and thought I might add my 'two peneth' of
knowledge: The idea behind all of these 'oven used' cooking vessels is
that the whole process of cooking is slow, and the effect on the food
might be compared to that of 'heat work' on pots in a kiln. The heat of
the oven will kill most germs (but I can understand peoples'
dislike/distrust of the patina or 'seasoning' that appears on the
cooking vessel); normal cleanliness aplies to these pots as it does
with cast iron, stove top, cooking pans and woks that have 'seasoning',
if in doubt slowly heat the pots (empty and dry) in the oven when using
the oven to do a high temp roast! Low temperature glazes will not make
the vessels more hygenic to use as eventualy all such glazes will have
some (albeit microscopic) crazing which can harbour debree/dirt, more
so than if left unglazed.
This method of cooking does add something to the flavour and texture of
the food; it used to be a great way to cook mutton (a tough but
flavoursome meat) but it's rare to find mutton anymore as most
suppliers sell only year old lamb.
Sincere apologies to any vegetarian readers!