All applicants applying for a .ie domain name who are not situated in the 32 counties of Ireland, must demonstrate a real and substantive connection with Ireland (with the exception of those applying by means of Community Trademark).
Examples of acceptable Documentation demonstrating substantial trade or commercial activity within Ireland are as follows:
Copies of invoices (showing trade to or from Ireland).
High-quality brochures showing a significant intention to trade in Ireland.
A signed letter on headed paper from a bank manager, firm of chartered accountant(s), registered auditor(s), tax consultant(s) (where the tax advisor identification number is displayed), or solicitor(s) confirming the applicants trade with Ireland....
.ie.nu is a company based in Dublin (in the popular tourist area of Temple Bar) selling subdomains of the domain ie.nu ; not to be confused with a real ccTLD. They just bought the domain ie.nu and sell subdomains of it. The price however is scandalously high. Plus, almost nobody in Ireland knows this (I lived there for three years and saw exactly 1! site using such an .ie.nu subdomain)
So why would someone consider paying a high price for some subdomain.ie.nu ? Who even guarantees this obscure organisation selling these subdomains won't cease operations in a while?
They started selling these subdomains for those wishing to bypass the restrictions on .ie proper. My advice: if you cannot get .ie, then accept that rather than wasting money on a subdomain.ie.nu