I have purchased two sets of these memory cards. The first set went into my 2008, 13" MacBook. I purchased a second card for my daughter's 2009 iMac because of the amazing performance boost I got on my MacBook.
Both of the aforementioned computers were running slow with OSX. The additional RAM was able to dramatically increase the speed with which our computers open applications, load web pages and save items on the internal HD and peripheral memory devices. Start up and shut down speeds are also dramatically faster.
If you have an older iMac or MacBook that is running one of the newer versions of OSX and you are getting the spinning beach ball/pin wheel, every time you execute a command, I highly recommend upgrading your RAM to the max that OWC recommends/offers.
BTW-installation is VERY easy. One view of the video tutorial and you will be an expert. FYI-I am 62 years old and I do not consider myself to be tech savvy.