I fully trust in the SlackBuilds provided by http://slackbuilds.org
and packages provided by AlienBOB http://www.slackware.com/~alien/slackbuilds/
and Robby Workman http://rlworkman.net/pkgs/
who are major Slackware's contributors.
Rule of thumb :
(1) never ever install a Slackware package if you don't know who is the packager.
(2) never ever install a Slackware package if the SlackBuild for it is not available.
I would check that before using the two last links you provided.