Hello. What is the safety advice on using 'dock a tots' for sleeping newborns? Thank you

There are a lot of portable sleep spaces on the market, which do not meet the Safe Sleep guidelines, including a number of safety concerns about pods & nests & on how they are used.
These include soft, padded sides & soft base & minimal height on sides.
Product Safety recommends sides of a bassinet should be 300mm high
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/bassinettes

Never place additional items in or around the cot, such mobiles, pillows (of any kind), bumpers, lambs wool, nests, positioners or thick loose bedding, even if the advertising looks enticing.
https://rednose.org.au/article/setting-up-a-safe-nursery-what-products-do-you-really-need 
https://rednose.org.au/article/baby-products-you-dont-need

Many of the pods/nests/co-sleepers have soft padded (cushioned) sides.(similar to a cot bumper)
Soft bedding is dangerous in a cot and should not be used. Soft bedding includes pillows, quilts, doonas, soft toys and bumpers. Soft bedding may cover the baby’s face and obstruct breathing and/or cause overheating.
https://rednose.com.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows

Lullaby Trust, our colleagues in UK, provides the following information about pods & nests P9:
Pods/nests Pods or nests are a softer type of sleep surface sometimes used instead of or in addition to a mattress, with areas that are raised or cushioned.
When sleeping, babies shouldn’t lie on or have anything soft around them, particularly their heads, as this can cause them to overheat and increases the risk of SIDS.
Soft, squishy materials can also cover baby’s mouth and nose if they are pressed against it.
https://www.lullabytrust.org.uk/wp-content/uploads/The-Lullaby-Trust-Product-Guide-Web.pdf