My first Mac Mini had a measly 1GB of RAM. It was enough to operate and become accustomed to using OSX, but was by no means a speed demon. When I purchased my second Mini, I ordered it with the stock 4GB of RAM. I knew that I could get RAM from any third party supplier at a much cheaper price. I was already paying the "Apple Tax" on the Mini, I didn't want to pay it on the RAM also.
I shopped around online at my few preferred vendors. But what I found when I arrived at OWC through a Google search impressed me. Their website allowed me to drill down my model of Mini to assure that I was buying exactly the right size, type, speed, etc. The installation videos they have available for all of their upgrades reaffirmed that it was an easy process. Their pricing was in line with the other vendors that I normally dealt with; and even provided buy-back for the RAM that the Mini shipped with.
I placed my order, it was shipped the same day and arrived promptly. In five minutes I had performed the replacement. If you're just checking email and browsing the web, you may not notice a big difference. But if you're using Office, Photoshop or Parallels then the bump from 4GB to 8GB will make a huge difference.
You can Google an find several sites that have done performance comparisons. You get the biggest improvement going from 4GB to 8GB, but not much more if you go beyond that. The RAM has now been operating perfectly in my Mini for nearly five years now. I would recommend OWC for RAM, SSD's and just about any other component you need to repair or upgrade your Mac.