Cuprinol do a black PRESERVER stain, which would soak into new wood well, and could be used as a first coat only, or the finish. Water-based.
I'm not actually recommending it, but Cuprionol Anti-Slip Deck Stain is available in Black Ash.
The ONLY reason I have mentioned it is because it's water-based, and shouldn't require too much preparation NEXT TIME you re-paint.
You will have to get the preparation right THIS time, but since you are having new decking, prep may not be an issue.
That said, I would ALWAYS sand a surface such as this before re-painting - it doesn't take long, and it's quicker to sand when the surface is reasonably sound, than it is on a flaking surface that didn't receive much prep last time.
Sadolin Black Superdec is a good product. Opaque solid finish. Water-based, resists flaking, usually requires a quick sand when re-painting. I don't think it has any anti-slip properties.
The point is, you should ALWAYS give the surface a quick sand at least before re-painting surfaces such as decking. It makes the paint adhere to the surface.
Of course, I would normally think to use an oil-based product, because it SHOULD be more hard-wearing, and do plenty of sanding and prep EVERY time to ensure a longer-lasting job.
It doesn't really make much sense using a water-based product that's going to be covered with rain-water, yet there are excellent water-based products ou there. I would rather do the prep every single time and use an oil-based product, or a decent water-based product.
That said, oil-based isn't fool-proof, and could still fail, like the others.
Some products, water-based or sometimes oil-based, can fail in a couple of weeks, and all needs scraping off and sanding well, and it's a complete drama. So you do need to research this well, and read any customer reviews.