It looks like the Cardone one has the extra mount point. The other "off-brands" do not. I wouldn't mess with the cheap ones anyways. This part number is specifically listed to only fit SLK32, C32 and SRT-6:
Product Detail

You can get it from Partsgeek for $101 but they wont ship to my APO box. The best I can find that will ship it is $200 from Amazon.