Are they equal in safeness? I was informed that using
<?= are called short open tags, and are not always enabled (see the
short_open_tag directive) with PHP 5.3 or below (but since PHP 5.4.0,
<?= is always available).
Actually, in the php.ini-production file provided with PHP 5.3.0, they are disabled by default:
$ grep 'short_open' php.ini-production ; short_open_tag short_open_tag = Off
So, using them in an application you want to distribute might not be a good idea: your application will not work if they are not enabled.
<?php, on the other side, cannot be disabled -- so, it's safest to use this one, even if it is longer to write.
Except the fact that short open tags are not necessarily enabled, I don't think there is much of a difference.