This is right on. I've been upgrading my Macs for some time, OWC is a great place to start for the basic upgrades that do not exceed what Apple supports for user level upgrades.
My current desktop is a Mid 2011 27" iMac 3.1 GHz i5. I upgraded to 32GB of ram from OWC. The only issue I had was one of the ram modules was bad- OWC next day aired me a new one. The iMac runs no issues with it.
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While it does void your warranty, and is not recommended by Apple, I actually swapped my HDD for 2 SSD's through OWC as well. Their videos made the process very simple, and they sell a nice specialty tool kit for the job. Before the upgrade, I did clone my current HDD to another HDD in case bad things happened. Two SSD's easily fit into the slot left by the HDD, using OWC's adapter. The swap to SSD from HDD significantly improved start up time and performance.