The SSD kit (with reengineered SATA cable still has straight connectors and a fairly stiff cable, but connectors ARE short enough to allow proper reinstallation of the motherboard without creating pressure on the motherboard itself) The power cable and sticky foam tape work just as designed, since the SSD has no moving parts, and hence no vibration. I pre-formatted the SSD with Yosemite in an external USB housing and was using it for a while before this internal installation, so I knew the SSD was working properly. While my mid-2011 21.5" iMac was apart to install the SSD, I also upgraded the original 500GB 5400rpm 3Mbit/sec Seagate drive to a 1TB 6Mbit/sec 7200rpm Hitachi drive using the full OWC HDD upgrade kit with tools and 2nd generation temperature sensor. So now I have a dual-boot system with two different versions of OS X: 10.8.5 on my 1TB hard disk, and OS X 10.10.3 on the SSD.
Patience is a virtue during installation. I also recommend wearing thin cotton gloves when removing and reinstalling the display panel. That makes certain that you will NOT get any fingerprints on the display surface. I also used a can of compressed air to remove accumulated dust from the fans, and a cloth to wipe the back of the display and internal surfaces that had collected dust during my first 18 months of ownership. The heat-generating components inside the 21.5" mid-2011 iMac require cooling fans and plastic shrouds to direct airflow. All those parts fit together with precision, and once taken apart, all these pieces will only go back into place with patience and a bit of fiddling. I found that removing the upper right of the plastic airway shroud behind the motherboard and then easing it back into place WITH the motherboard during reinstallation made it much easier to return everything to the proper location so the motherboard assembly could be aligned and screwed back into place. The installation process is not particularly DIFFICULT, but there are many many steps and many thin wires and cables with tiny connectors that first must be carefully disconnected when disassembling, and then carefully reconnected during reassembly. Yes, they COULD be damaged if mishandled. If you are experienced in taking modern computers apart and reassembling them, then go for it.
It is a HUGE help to have another computer right there to play the OWC installation videos available on YouTube. I had my retina MacBook Pro on the desktop beside me, and was able to view and replay the video as often as needed. In all, I took my sweet time and spent about 2 hours doing the dual upgrade - SSD and hard drive with OWC sensor cable, not including time spend installing Yosemite on the SSD, nor cloning the original HDD to the new one. Reinstallation went smoothly. I plugged it in, turned it on, and the dreaded 3 beeps! I somehow managed to transfer a tiny bit of the adhesive from the SSD foam tape onto a finger and onto one of the RAM module connectors. Powered off, and a quick inspection and thorough cleaning of the RAM connector, reinstalled, and the system booted normally. Then I noticed a tiny dark semicircle at the bottom right of the screen near the Trash icon. I wondered how I could have cracked the display glass in such a perfect semicircle while gently wiping with the lint-free cloth. I used the suction cups to again remove the front glass panel for a closer inspection, and reallized I had gotten a piece of blue thread (from the lint-free microfiber cloth, apparently) on the display. A flick of the finger, and it was gone.
