This is interesting, because for all those opinions stating how you should not/never feed a baby under 6 months solids, what can be said of the fact 6 years ago, when my DD1 was born and 8 years prior when my DS was born, we were advised and strongly encouraged to start weaning our babies at 4 months old? So both my older kids had rice and pureed fruit & veg from 4 months and by the time they were 6 months old, they started on finger food. So have I and the thousands, maybe millions of mums caused their babies harm?
I started giving my older children, and DD2 pure baby rice once a day (just a teaspoon full of rice mixed with milk) for about a month, then I gave her pureed carrot (just a little), and just yesterday I decided to add a little pureed fruit to the baby rice. Baby's digestive system needs to get used to the new food, so I don't add new foods for about 5 days at a time. My 5 months old is now on 8oz milk (just this week). She has them at about 3am, 8am, 12pm, 4pm and sometimes she has another at about 8pm (though not all of it). She should ideally be on 4, 8oz milk feeds and some pureed food/rice, rather than 5, 8oz milk feeds. the HV said she's definately ready for weaning.
Research is always ongoing. Problem is, a lot of people wean their babies by giving them pureed versions of their meals rather than pureeing say one veg and giving that for a few days, then trying them on another, then another, etc., and slowly introducing a very small amount each time to allow their gut to tolerate it. It's probably safer to encourage weaning later in that case, but, harmless for those who very slowly wean their babies.