It's not a POS because of the flats. May be for other reasons, but that isn't one of them. It's a function of the distance between the bending rolls. The flats occur because there is nothing to bend against on the ends until the material contacts both rollers.
Your best option for nice round rings is:
1. Cut the material to length- figure the circumference of the finished roll through the neutral axis- that is through the centerline of the material. If you were rolling a hoop out of 1/4" stock and wanted a 8" outside diameter, you would subtract one material thickness (half the thickness from each side) from 8"- then multiply that by pi. In this case you would cut the strip to 8" minus the .25" material thickness=7.75" X 3.1416 = 24.3474" long. If you were using 1/2" stock you would use a strip 8"-minus material thickness= 7.5" x 3.1416= 23.562" long. Take a few minutes to do the math. Get the length right, DO NOT leave extra and try to roll a double thickness through the rolls. It will ruin any set of rolls, not just the cheap HF version.
2. Pre-bend the ends back before rolling. Do this for the distance between the bending rolls plus an inch or so. Make a cardboard template of the inside diameter, and check to see that you are close to the inside radius you want. Again, this will vary due to material thickness. Do the math.
3. Roll the ring as usual, until the ends come together.
4. Tack weld the ends together while still in the roller. Grind the weld flush so you don't damage the rolls.
5. Without changing the roll settings, roll the now-tacked cylinder around a time or two. Back-roll if you can.
6. This should net you a near-perfect ring, spot-on dimensionally and ready to use.
Good luck.