A performance difference. That depends on how much you use your mac. But for me I don't use it all that heavily. Just a few basic apps + photoshop and garageband. And amazingly the perfoemance gain was rather good. Not a faster mac or anything but apps opened up quicker and ran smoother and less spinning beachballs.
Basically with 1GB I had a lot if page ins and outs to my hard drive. But with 2GB I have nothing paged out to my hard drive.
Would you see a major difference in performance? I would say you would see some performance, little or big. But going to 2 GB is really useful. I would really recommend it.
And to answer your question would it work. The ram you are showing that is with the white imac. I say it will. But also here is a review on that site for the ram.
I bought this product to replace the 1GB of RAM already in my Apple MacBook. With 2GB of RAM, MacOS X runs far more smoothly, with less beach-balling. Great product at a great price.
Sure that's a macbook but the imac uses the same ram. So it seems others have successfully bought this ram from this place and put it in macs.
And enjoy the extra ram if you choose to get it.