This is a common misconception. It's important to be aware of what are often referred to as Internet experts, who mistakenly assume that a product that's already crash-tested has to be tested in ALL car seats.
Fact: The Snugglebundl is actually a garment that wraps from the back and ties at the front. It's less than the thickness of some baby-gros. It is called a blanket because it's like a shawl to emphasize its coziness. Legally and in usage, it is classified as a garment.
Fact: No baby garment is required to be crash-tested. The fact that the Snugglebundl has been tested at all is purely to provide further reassurance to parents.
Many internet experts seem to assume they know better than the leading car seat safety experts who have actually inspected the Snugglebundl, including NASA crash testing experts who carried out the crash tests.
Many internet experts assume that car seat manufacturers stating that they do not recommend products they haven't tested is confirmation that a product is unsafe. This is, in fact, misinformation because no car seat manufacturer can test all garments worn by babies in car seats. What they do recommend is that the baby wears fewer layers, and clothing is safer if it is thin, dense material with no front or back padding, especially around the chest/torso area.
The Snugglebundl is not only made of thin, dense organic cotton material with no padding, but in a three-point harness, the straps go directly over the baby and the sides fold on top of the straps. This reduces the need for extra layers under the straps, which would otherwise be thicker than the Snugglebundl itself. This gives it a minus fluff factor!
Snugglebundl Ltd likes to stick to the science over opinion, which is why they crash-tested their product and had it inspected by leading car seat experts.
There is a lot of Internet misinformation, even from car seat fitters who haven't physically checked certain products, including the Snugglebundl. Some even sell their own garments, which can affect judgment.
Snugglebundl has sold well over 100,000 units to very happy parents and regularly receives 5-star reviews. It has won awards as a car seat accessory. Talking to actual Snugglebundl owners is the best source of information you can get.
Thank you for your interest, and please stay safe.