we sent our girl to parkside montessori on inwood ave (between park and valley). it is wonderful and the girl really, really loves it. she's always had shyness issues but has seemed to blossom there and the teachers always speak highly of her and they are very good with keeping us updated on progress and issues. her cousins both went there and they loved it and their parents loved it as well. they are both doing well now in the montclair school system. the head person there, ginger, is very good at being honest with her evaluation of the students and their potential in higher schooling like kindergarten and won't hesitate to recommend holding a child back if she thinks they are not ready. i can't really comment regarding the actual teaching method since i have nothing to contrast against. i can tell you that the girl at 3 knew all her letters, could read and write them, knew all her numbers (0-9) could read and write them and really loves going there.
our neighbor sends her girl to union congregational daycare which is not a montessori school and she's not so happy with the teachers there. they rarely give her any concrete information about what they are doing and don't give updates other than "we think she is doing ok".
granted this information isn't really about montessori vs. non-montessori but more parkside vs. union cong.
from what i've read, however, montessori is very "learn at your own pace" which we prefer.
pm me if you have any other questions like price, scheduling, etc.
EDIT: we started sending her at 2.5 yrs and she was the youngest and smallest in the class