As far, as i know, iMac uses RAM modules, that are mainly for notebooks.
Will this module work ?
Which iMac do you actually have? It looks like the 21.5 could be the screen size and if so there are only a few real options...
Crucial have a great memory selector that features a good few types of iMac and so I'd look there. They have the option of scanning your system to find out what memory is needed but I don't know if it works on a Mac.
The options I've listed look the same as your one, just $5 cheaper, and Crucial are just as good as Kingston for memory in my experience.
If you give more details of you system so we can narrow it down then I might be able to say for certain if it's the right memory for your machine.
From what I can tell from Google, which isn't much as details of iMac MB950 internals seems to be pretty scarce, the memory type that you listed should be compatible. The Crucial equivalent to your one is this one.
As I don't own an iMac I can't guarantee it will be right, just everything I can find about it shows that that memory looks right to me.
I found a user manual and apparently you can open up the memory bay. May be worth taking one of your sticks out and double check that, usually they have some vague identifying marks that should show things like DDR3, SO-DIMM, 1066 and so on. If those three things are on it then that memory should almost certainly be fine. Take care not to directly handle the contacts on the memory (may be worth reading your manual to see what they recommend) and only hold it by the edges, the idents usually look something like this: