I have an early 2009 iMac, 24", core 2 duo, 2.66. Will this RAM fit? Moreover, will it work?

The provided RAM is compatible with Apple Macbook Pro "Core 2 Duo" 2.66 13" Mid-2010. There is no information indicating compatibility with an early 2009 iMac, 24". Therefore, it is unlikely to fit or work with your iMac.

Did I make a bad purchase? Should I have bought the OWC upgrade kit instead?

Worked just great for me. No issues and cheaper than OWC.

Questions & Answers: CMS 16GB (2X8GB) DDR3 8500 1066MHZ NON ECC SODIMM Memory Ram Upgrade Compatible with Apple® Macbook Pro "Core 2 Duo" 2.66 13" Mid-2010 - A15

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CMS 16GB (2X8GB) DDR3 8500 1066MHZ NON ECC SODIMM Memory Ram Upgrade Compatible with Apple® Macbook Pro "Core 2 Duo" 2.66 13" Mid-2010 - A15

Computer Memory Solutions guarantees compatibility with models provided in description.
Memory Type: SODIMM, 204-Pin
Speed: DDR3-8500, 1066 MHz
2 Piece Kit
Product appearance may vary. Picture for reference only. limited lifetime warranty when bought directly from computer memory solutions

$37^.50 –