I send my 2.5yr old daughter to Q-Dxx mid last year, now it's her 2nd year there already
Beginning of this year I also send my 2yr+ son to the same school, now already half year there.

From what i see, they've learn a lot, and I mean A LOT during their school days, they are more independent now, now both of them can hold a pencil properly, and my daughter can write 1-10, A-I without any help at all

Initially both of them get sick quite frequently coming back from school, it's due to most of the time they are holed up at home, with limited contact with other people besides their immediate family members.
My mom actually objected to send them to playschool/kindie so early, as they get sick all the time, but I strongly believed that kids should go out there to mingle with as many people as possible, and yes they'll get sick pretty fast, but that's just the initial stage to build up their immune system.
And now, after my mom sees the drastic change to her grandchildren, in terms of health, language mastering and other things, she even encourage other relatives to send their kids to pre-school/kindie as soon as possible.