Lol. Any linker is not safe
Because obviously they just do the same thing, load and execute the written scripts.
Any form of worms/malicious codes will have a hard to time to spread because there is no fixed AJAX function to spread the script. And anyway, this linker has been used before. In every linker we use, the danger is always there.
But I reckon, there is a more dangerous linker than this. And it's currently working right now.
And by the way, the media box linker (moz-binding and expression) is still working.
[spoiler]Paste in media box<">[/spoiler]
Though the advantage of the linker in the first page is that it's faster than moz-binding/expression and it works cross-browser.