If your 2019 iMac 5K has only 8GB memory, this lets you easily upgrade to 16GB and see performance improvement.
Installation is easy, requiring no special tools. Remove the memory cover on back of iMac. 2 of 4 memory slots will be empty, install these and replace cover, Boot to see 16GB. Search iFixit site for more detailed instructions.
These 2x4GB memory sticks were was removed almost immediately from a new 2018 Mac mini to upgrade that system to 32GB.
The 2018 mini uses the same PC4 2666MHz 260 pin SO-DIMM as the 2019 iMac.
