I don’t understand comments I see about the Dock a Tot

So many mommas I know have recommended the dock a tot to me because it worked wonders for them and their little ones - from co sleeping to lounging etc.

Someone bought me one earlier in my pregnancy and I was super excited! Then I read a ton of mixed comments regarding the DOT on here. Most women seem to love it but a good handful say its not safe. But I don’t understand. If the baby can not roll yet and is laying on his/her back - how is it unsafe for co-sleeping? I just don’t get it. 🤷🏼‍♀️ do you think I should return it?