Why should I use Iesi.Collections instead of the traditional System.Collection?

Question

Was research on how (for convetion) define a Many Many where table where both fields are primary key and found this post.

So decide to install the Iesi.Collections in my library domain.

But there came a doubt. In the "Iesi.Collections" outperforms "System.Collections" Iesi.Collections? Why should I use?

It is better in performance?