php process xml readfile

Here http://ift.tt/1BMUK5G read that to get xml content better to use readfile, because it is the fastest.

I want to get and process content from here http://ift.tt/1zgwGUJ

I did

readfile( "http://ift.tt/1zgwGUJ" );

Then if result contains word no I will continue.

Like

if( strpos( 
readfile( "http://ift.tt/1BMUK5K". urlencode(get_ip_address()) ),'no'     
) === true ){
echo ' continue<br>';
}

But it does not work. As understand readfile as if echo content of the file.

Do I need to use file_get_contents (can not do it with readfile)?