@Macit will probably provide you a complete answer, but some of it you can get easily from the extension setting at Dofo. e.g.
https://dofo.com/extensions/io
tells you there are 483k registrations in .io, of which 36k are for sale currently on marketplaces. It has a Global Rank of 52.
It also will show you the most popular sites in the extension, as well as registrar and country breakdown.
If you click on More Filters, you can limit sites with websites to get that data.
I too would like to know how you access the Alexa data from the various classes e.g. top 100k for an extension. I don't think I know how to do that.
Of course whether it is a good extension for a
personal brand is a different one, although I agree related, to how many registrations, websites and popular corporate sites there are.
Bob
PS When Dofo give the Global Rank,
@Macit, is that simply based on number of registrations, as opposed to the Cisco Global Rank? It seems so, I see .co is Global Rank 19, .me is 38 and .io is 52, but I think that is simply registration based.