Well, it works as it can be seen from the tutorial. You’ll need to provide us some screenshots showing the steps you took if you need help troubleshooting.
To be clear, here’s what you need to do step by step:
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Migrate one of the UE Mannequins including their dependencies. You can create a new project with the Third Person Template, and all of the dependencies will be selected when you right click on the SKM, then Asset Actions > Migrate. (If you like you can exclude unnecessary stuff such as textures tho. But make sure to include the Skeleton, SKM, and the rigs) After that, all you need to do is to hit OK and select the Content browser of your existing project.
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Create a new Animation Blueprint for the mannequin (or use the existing one if you migrated that too) and plug the Control Rig node into the main Out Pose of the Anim Graph. The tutorial also shows how to add that Should Do IK Trace pin.
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Now that we have a character that has IK feet, we can move onto replacing the SKM with a metahuman. Follow the tutorial to see how to add a metahuman to your project, and copying the Skeletal Meshes into our existing Character Blueprint. Then you just set the leader pose, hide the original SKM, set the bones to always refresh (again, you can see how in the tutorial) and that’s it! Now you have a metahuman with IK feet
Hey something just came to my mind. Perhaps you didn’t select the CR asset from the Control Rig node 
I suspect that might be the case since you also mentioned A pose. Like I said, I’d recommend first following the both tutorials carefully, and then sharing the steps you took in detail with us if you encounter any issues.