My dd is in a unit like this except that there are 3 classes worth - ie 90 kids! I have to admit that I was absolutely horrified when I first realised how it worked but 2 terms in I'm becoming a bit of a fan! Did (reasonably shy, slightly quirky, not great with loud noises, academically able) seems to be both very happy and thriving there.
There is a "quiet room" that is about the same size as a carpet area in a normal reception class so sometimes classes or small groups go off there to do activities. The room is purpose build and enormous and I was amazed how calm and quiet it was when I visited. They have classes and they split off into their classes for phonics and numeracy plus some other activities each day - two classes have a carpet and the third (dd's) uses the quiet room.
There is a big, easy access, purpose built for Foundation stage kids outdoor space.
The advantages of the system seem to be:-
The unbelievable choice of activities. They have a woodwork area!
It works well for dd who is academic as they seem to be grouping by ability when the TA takes them off for activities. She is in a group of about 8 who seem to be doing extension activities whereas in a class of 30 she'd be one of 2 or 3 of that ability so would have less time with the TA.
It also seems to work well for a slightly quirky child. Dd always always wants to do drawing and writing when it is free choice. Before she started (she was like this at nursery too) I had images of her sitting all on her own. But with 89 other kids there is always someone who wants to do drawing and writing too.
There does seem to be less girl friendship issues than in a smaller "class". I have a friend whose daughter is in a lovely village school with a class (and year) of 22. In the first term there seemed to be a lot of problems with friendships amongst the girls as they were all jostling for the "Queen Bee" place. With 90 kids and 40ish girls there seems to be less problems as when dd and her pals have there inevitable "I don't want to play with you" falling out she just goes off and plays with someone else. The children she invited to her party were about 2/3rds her class and the other third a mix from the other two classes.
The teachers seem happy. Quite a few of the mum's in dd's class are teachers / TAs in other local schools and some have said that as a teacher if you like the system then you will really like it as quite a bit of the lesson planning etc is more efficient.
The downsides:-
The "class identity" seems less strong than in other schools. I was looking forward to no more party invite angst as you just invite the whole class and lots of mums nights out. That doesn't seem to have happened.
There is still a tiny bit of me that feels uncomfortable that my tiny precious baby is one of 90.