It has been fantastic for my daughter, who is 4 later this month. She was an early talker so started there at 23 months and has absolutely bloomed. She goes 2 mornings a week and then does 2 mornings at a normal nursery which is obviously more 'play' orientated.
She can now just about read and write and I am sure that Montessori has helped a lot with this.
My son is 22 months and is talking very well too, so we plan to send him after xmas. He went last week for a trial day and loved it!
I do think some kids will benefit more than others, and obviously there will be big differences between the schools/staff etc. I am unsure my son will benefit as much as he is much more of a 'boy' whereas my daughter is a bit of a swot and gives herself homework!
Would be interested to hear what 'damage' it did to your son THS.
The govt. scheme did contribute but it is more expensive than the normal nursery. From memory it is about £500 a term for 2 mornings a week, whereas the other place is £200 for the same time.
I get the nursery vouchers through work which saves 40% so is worth doing if you can.