Some observations about differences between the Early Years Foundation Stage (EYFS) - i.e. standard nurseries and reception) & Montessori:
IIRC, EYFS recommends that all childen should have access to the outside at all times if possible. Montessori doesn't.
My DC's reception class in a mainstream primary was a wonderful place of free-flow learning, with activities set up around the class and outside designed to appeal this specific group of kids. (They visited us all at home before the DC started school and found out what their interests were so they could do this.)
The children could choose whether they learned inside or outside, and there were tasks set up outside to suit the children who liked to be active and noisy, as well as calmer activities inside for the DC who likes to learn quietly and calmly - unlike the Montessori that only catered for DC who knew how to sit quietly all day - an unreasonable ask of nursery & reception age DC if you ask me!
The Montessori was much more rigid. All the DC were sitting at tables for one, or on mats, for one. They had the choice of which bits of equipment to use (Montesorri standard, only), but it was clear that they were expected to get it, come back to a space for one, and interact with it on their own, not play with others. I noticed when DC did play together, the Montessori teacher subtly stopped the play. I don't know if it was just this teacher or if this is typical but I found it controlling and stiffling of creativity and play.
For example, two girls started playing and dancing together. The teacher stopped the whole class, stopped the girls' game and brought them all together in a circle so they could take turns to go into the circle one at a time and dance. I was annoyed for the girls, they were having a lovely game together, it really didn't need the teacher to formalise it.
Similarly, a child wanted to roll around with one of the little mats, pretending he was a sausage roll. It was, again, a bit of spontaneous creativity. He was gently encouraged to stop too. Another boy wasn't using his equipment in the "correct" way, so he was gently guided to do so.
There was no home corner, no book corner, no messy play, no free flow to outside, no groups of children playing together. It was so controlled, free play and genuine creativity was squashed. I absolutely hated it. And I hate to think how a noisy child who needs a lot of exercise and stimulation would fare there. Not well, I imagine.
The one that was mixed Montessori / modern methods seemed a lot better than the strict one, which was just unnecessarily dogmatic IMO.