Sorry come into this so late!
Well run by properly trained staff, Montessori can really work and be a wonderful introduction to schooling for children in general but I have heard of a fair few horror stories to date about nurseries with only 1 qualified staff member there, who don't monitor the children enough and leave them completely to their own devices. 1 child I know got a kidney bean stuck up his nose and was very lucky to have survived as it swelled up in the nasal passage and wasn't spotted by staff until the end of the day when he was struggling to breathe! He was 2 1/2 at the time.
Ofsted pretty much passes most nurseries from what I gather, regardless of whether they are good or bad and it's down to the parents and you as a potential new recruit to find a good one to start in.
To call yourself a Montessori school, you only need 1 trained person on board, this is somewhat different to what parents expect. It often seems to be an excuse to bump nurseries fees up without actually providing the extra - that was from the mouth of one of the Chairwomen of the Montessori Education UK who runs her own (particularly well I must say)!
There are also several outdated ideas being used with children in the Montessori setting - i.e. the use of Brasso for polishing when it is a seriously toxic substance which causes lung disease and damage to the central nervous system if ingested - why can't beeswax be used instead?!
The ethos of Montessori is a wonderful one, done properly I believe it's hard to beat but it's not always done properly and that's where it all falls down.
I've had a really seriously bad experience with the Brighton and Hove Montessori myself but in the past I've experienced a brilliant nursery for my older children (now 20 and 19) so I appreciate it is not an indication of how they all are.
I would agree with training on a wider scale and getting the best of all worlds, pure Montessori can prove challenging in this day and age and it will enable you to get a better job long term if you have a broader spectrum of training.
Good luck with it though, I'm sure with you being so interested in finding the right course for yourself that you'll do brilliantly!