During the day when the baby is supervised and taking a nap using a sleep positioner is safe and okay for the baby.
However at night when the baby is not gonna be supervised the sleep positioner for the baby is not safe and poses a risk of SIDS for the baby.
There have been some babies who have died as a result of sleeping in a sleep positioner at night so do not leave the baby unattended when sleeping in or using a sleep positioner.
In fact it's best to not even use a sleep positioner at all because they really are unnecessary and are not worth the risk.
Just have your baby sleep on a firm baby bed crib mattress without any crib bumpers or pillows or blankets.
If it's cold or cool in the babies room put the baby in some blanket sleepers to keep them warm.