I've been in one for a month and will start a year next semester. I can't speak for all of the schools using the system in China, but the one I am at is very nice, but as with anything, has ups and downs.

A big up would be that in general the kids are given the space to roam free in a constructive environment. In the first kindergarten I worked in the children were told when to drink water, when to use the toilet, us teachers did everything for them, but in the Montessori the children of the same age are much more mature, my first day of observation this was very clear, a boy no older than three years old juiced an orange, a young girl the same age trimmed the flowers, then arranged them into a bouquet. All on their own account.

As for a downer, I would say resources, in my school some classes are loaded with Montessori resources and some are bare, ask the school for resources and they say think about what you want, go online, print it, and be done with you. Also as with any school I have been in it can be hard to get information in a timely manner.

Feelings, the one I am in is of a better standard than many of the kindergartens I interviewed for, and by far the best school I have worked in. Though my experience is limited, I don't a huge range of schools to compare.