So, um... wait... why does it support stuff that exists only in Icelandic but doesn't support, like, Portuguese letters?
Useful if you need to combine programming with some typing in one of the very few languages that it supports - and even then you have to teach yourself anew where your letters live now. (Quick, where's Å?)
Yes, the **** that passes for "US-Intl" layouts in the Linux world is all Microsoft-inspired and useless to programmers, and it's near-useless for typing plain English text too. They could just copy Apple's approach to structuring US-Intl: basic and shifted keypresses function 100% identical to plain US layout; alt-presses and alt-shift-presses give you a million accents as dead keys, plus a million letters and symbols that aren't part of the plain US. Way more general solution than this.
If you want to remake that thing for yourself on Windows (and you have an hour to spare) just download Microsoft Keyboard Layout Creator. I'll never understand why that program isn't super-famous.
Edit: ha, okay, I see I spilled some vitriol a little rashly - it's actually possible to type Portuguese on that, like... Alt+Shift+6,E gives you Ê. Hmm. Nope, not handy.