S.P.
I think that the individual Montessori program makes a big difference. There is no licensing requirement to be "Montessori" and anyone can use the name, or call themselves "Montessori based." My daughter is a Montessori daycare, and so far we're very happy. The idea that there's NO structure is not true in a real Montessori environment. And the children are self-directed to a large degree, but the teachers encourage them to explore different areas. Montessori strongly pushes internally based discipline, and many kids come out with a much greater ability to focus. However, it does encourage individual work, and may not be the best choice for all children.
My suggestion - do research and visit the schools. Montessori is only one option, and it should be mostly about finding a good fit for your child. We didn't choose our daycare because it was Montessori, but because the calm, respectful atmosphere impressed us, and because they had a great physical space and great playground. It "felt right" for our daughter. We visited/talked to other Montessori (or in one case "Montessori") schools, and I can say definitively that there's a BIG range out there for things that call themselves Montessori.