Differences between HDD Cage Kits ?

Hi,

We'd like to add additional HDD cage in ML350p Gen8 (we already have one, 6 LFF).

Which one must to use, there are two alternatives found:

659485-B21  5U 6 LFF Hot Plug Drive Cage Kit  or
661717-B21  5U 6 LFF Expander Hard Drive Cage Kit ?