advice SEO optimisation for landing pages

A small description is always better than nothing, but the more content the better.
Usually, landing pages don't rank very well.
There is more to consider than just content, there are also the titles, image (with alt, title attributes), semantic, no content stealing (alias duplicate content), and even more

Thanks Gube, totally understand. It doesn't look like we can amend title etc, so I suppose these landing pages are very limited in terms SEO optimisation.

In terms of Dan itself, if someone was to search for 'Crypto' for example, could a better description here move it up in the search results on the Dan page, or are they purely ordered on similarity to the searched for word?

I can't say for sure, because I've never taken the time to add descriptions to the DAN pages, but my guess is that the search would be based on just the domain name and not anything else on the page. I am not sure if google and bing would index the dan landing page, but they probably would, especially if you point the DNS there for a long period of time, like 2 months minimum, and in that case, it would probably help to have a description. But like Gube said, they will probably penalize you for having a landing page that they would consider low content or duplicative or whatever. Advertising remains a huge challenge in this industry.

That would just about cover it as if it isn't your own hosting you have no control to do anything more.