At present, the most direct URL to Eiši.com is http://heima.olivant.fo/~egilstro/ei%F0i.html. At some point in the future, that URL may change. The URLs http://xn--eii-4ma.com/ and http://eiši.com/ are forever.
Our recommendation is to link the most direct URL, but keep some documentation of the future URL.
E.g. a link like this:
Eiši.com,
which is coded as
<a href="http://heima.olivant.fo/~egilstro/ei%F0i.html"><!-- If not found, see http://eiši.com/ -->Eiši.com</a>,
Webmaster: styrheim@post.olivant.fo