To my surprise there was no comparison. My magnifiers worked better for me than the readers. I have been doing pulled work on 60-70 count fabric and I couldn't have done it without magnifiers. The magnifiers actually make the tiny threads and holes a bit bigger and I can see exactly where the needle has to go in.
I know several embroiderers who use readers quite successfully with their specs. Perhaps I am past the stage already where clip-on readers will improve the vision I have with my specs.
The optometrist acknowledged that they couldn't improve my vision with their readers and graciously made some adjustments to my magnifiers so that they don't flip themselves off my specs when I least expect it.
I asked about the difference between magnifiers and readers, but all I learned is that a "2x" magnifier does not relate in any way to a "+2" reader!? They are different. Perhaps it has to do with the magnifiers being situated a little distance from the spec lenses while readers fit right next to the lenses?
But then I don't really need to know the answer to this to do my embroidery, do I? All I can say is its important to try out various options and see what works best for you.