If you need a compatible SSD to use with the hardwrk SSD/HDD-kit, we can recommend the following items. Our experience shows: better go for a solid-brandname SSD instead of an overbreed no name special-manufacturer SSD. Total black-outs and little surprises regarding the stability are the order of the day for most no name manufacturers. For your MacBook (Pro) you will not need any special accessories, so just order the basic version of the SSD.
Since the SATA2 standard is outdated and SATA2 SSDs have become pricy we do only recommend SATA3 SSDs. They are working in every MacBook (Pro). The Samsung 840 series has been replaced with the EVO series which achieves even higher write rates as their predecessor. Furthermore the EVO is the first SSD to provide 1 TB capacity at a reasonable price. Yet the EVO is a bit more expensive than the 840 series it still is our recommendation. Even faster, but more pricy as well is the 840 Pro series by Samsung. For all of you working with large amounts of data on a professional level, we recommend the Crest for Mac by Angelbird. Next to out of the box Trim support it also scores with emergency power supply and is the only consumer SSD that provides this.
For the use in your MacBook (Pro) we recommend the silent HDDs by Hitachi (500GB/750GB) which Apple also often places in their MacBooks. If this is not enough space for you, pick up a Samsung or WD disk providing up to 1 GB of space. Keep in mind though, that in most cases more space also often means a louder and more energy consuming drive. So you should think twice if you really need an 1 TB disk in your MacBook (Pro). We strongly advise against the by now available disks with 1,5 TB capacity.
Our tip: Better go for a disk with 750 GB and 5.200 RPM than for a 1 TB disk with 7.200 RPM. The difference is not that much in an SSD/HDD combo and in most use cases not relevant.