Security I believe security concerns are irrelevant here as the code is "approved" by LJ and the only control that the user has is the userid. The code by itself is just a script to dynamically call a piece of text from BlogSpan. Totally harmless.
Load I doubt if this will result in an extraordinarily high server load due to increased traffic.
Benefit LJ users can discover other journals and other non-LJ users will discover theirs. This is all in the spirit of growing into a community.