Spikes Lowers Question

OK I am looking at some Spikes lowers on their website http://www.spikestactical.com/z/index.php?main_page=index&cPath=104_65 and see one ST-15 at $179.95 then right below it, an ST-15 for half off… Any idea what the difference between the two are?

Could I go with the %50 off and do just as well as the full price one???

Thanks in advance!

Brian