I think embroidery hoops are wonderful. They allow for superb tension and, when you use them with a table clamp or seat frame, you can use both hands.
If you are buying one, check to make sure that the screw for the outside hoop is notched (sorry, don’t know the proper term), so that you can use a screwdriver. Then you can get your piece “drum tight.”
You can also bind the inner ring with bias tape for even better tension and for more protection for your stitching.
When you are done stitching for the day, you remove your fabric. You won’t get marks. With respect for a previous poster, a hoop can’t cause your thread colors to bleed.
You do have to think about the order you stitch in. You can’t put a hoop directly over beads, sequins, etc., so do them last.
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I have hoops in different sizes and try to use a hoop big enough to hold most or all of the picture Im stitching, this way I dont really need to move it and risk flattening the stitches - but even if I do this, I can wash the project when its done and the stitches will un-flatten themselves.