What do you think of sleep positioners for babies? Many of my friends swear by it to prevent flathead and correct positioning and prevent SIDS

I think it depends on the baby. We had this for my son but he absolutely hated it and hated that he couldn't move around. Plus, I feel that he would outgrow this pretty quickly. If I remember correctly, it's about $100+ at Takashimaya so it's quite expensive for me. Sure, it's a good preventive measure to prevent SIDS, but I feel that an empty babycot that has no obstruction is just as fine.