Is it better than hyaluronic acid?

It is hyaluronic acid, modified. The case for it is retention rather than more hydration, and most of that case is supplier data. Plausible, not demonstrated.

What does acetylation actually change?

It replaces some of the chain's hydroxyl groups with acetyl groups, so the molecule stops being uniformly water-loving and gains some affinity for the skin surface.

Cosmetic hyaluronic acid is made by bacterial fermentation rather than taken from animals, and the acetylation step adds nothing animal-derived.

Can I use it with retinol or acids?

Yes. There are no documented conflicts and no reason to separate the steps in time.

Do I still need a moisturiser over it?

In most climates, yes. A humectant does its best work under something that slows evaporation, and that is truer the drier the air is.

Sodium Acetylated Hyaluronate — Ingredient Guide

How it works

Hyaluronic acid is a long chain of repeating sugar units, and along that chain sit hydroxyl groups — the parts that make the molecule so thoroughly water-loving. Acetylation swaps some of them for acetyl groups. The chain still holds water, but it is no longer uniformly hydrophilic, and that mixed character is the whole point: a molecule with both water-loving and less water-loving regions has more affinity for a skin surface that is itself part lipid.

What a formulator is buying is substantivity — the tendency of a material to stay where it was put rather than rinse or evaporate away. Plain hyaluronic acid draws water into the outer layers and gives it up again as the air dries; the acetylated form is described as holding to the surface for longer and surviving contact with water better. The backbone is made by fermentation, as cosmetic hyaluronic acid generally is, and the acetyl groups are added afterwards in a chemical step.

The evidence

The parent molecule is on solid ground. Topical hyaluronic acid at a range of molecular weights measurably increases stratum corneum hydration in the short term, and that is one of the better-supported claims in cosmetic science.

Evidence specific to the acetylated derivative is thinner. Most of what circulates about it comes from the companies that sell it, which is not the same thing as invented but is not independent either. Nothing about the modification is implausible — the chemistry does what chemistry of that kind does — but “better than hyaluronic acid” is a comparison, and that comparison has not been settled in the open literature. The honest position is hyaluronic acid with a plausible retention advantage.

Suitability

Suits every skin type, including oily and acne-prone, since it hydrates without adding oil
Most worth seeking out if plain hyaluronic acid feels short-lived on you, or if you live somewhere dry
Usually blended with other hyaluronic acid forms in one product rather than used alone
Not an active: it hydrates, and it does not change how the skin behaves

Concentration

No figure is quoted. Materials in this family work at fractions of a percent, and the useful level depends on molecular weight and on what else is in the formula. A product advertising a large percentage of any hyaluronic acid is describing its texture rather than its performance — past a point, the only thing that increases is stickiness.

Conflicts & combinations

Nothing conflicts with it and it can sit under or over anything. Like every humectant it does more with something over the top: in dry air a hydrating layer left bare has less to hold on to, so a cream or an occlusive afterwards is the standard move.