DD, now nearly 4, went at 13 months (I took a year's maternity leave and then tacked on all my accrued AL).
She's always done 3 full days. I chose a small, independent nursery with low staff turnover.
There have been pros and cons.
Pros:
-socialisation. DD was a pandemic baby and an only child, no other children in the family. The social aspect of nursery has been great for her development
-activities she enjoys but that I wouldn't be keen on doing at home, such as messy play and digging about for worms
-both DH and I have been able to keep working and my career has really taken off, which is just as well because the cost of living crisis hit just after my mat leave ended
Cons:
-food not great, lots of processed stuff like fish fingers, sausages and burgers often on the menu
-the first year we had back to back illnesses including trips to the hospital, she would get well, I'd send her in and a few days later she'd be ill again. This is because people send their children in ill all the time, some are even on antibiotics (I've seen the staff's medication list).
-at 1 you can't really make them understand that you're not abandoning them and will come back for them soon the way you can explain to a child over 2, for example. That makes leaving them hard.
Knowing what I know now, if I have another I'll look into unpaid leave or other solutions to enable me to stay home longer, maybe until 2. Personally I wouldn't send in a baby under 1, the baby period is crucial bonding time and also the attack on their still fragile immune system is brutal, babies deteriorate much faster from illnesses than older children. This is just my opinion and I'm not judging anyone else's choices though.