I used to make circles back in the 70's by putting a thumb tack stuck down with tape and point pointing up. Place the middle of the fabric on the tack and sew away. I do not think they had a tool/attachment back then. Since I do not sew enough circles to buy the attachment, I will stick with my old way.

Sounds very much like Rotarians

Using pinking shears to cut around the circle helps the turned edges to be smoother.

A lot of people still use this method--is it basically what Vikings attachment was until they improved it.

This Jenny Doan's tutorial on using her circle magic. https://www.youtube.com/watch?v=3gKvdrexKE4

It is important to clip the inseam properly. Are you making little "v" snips around the seam? This will compensate and smooth out most of the imperfect sewing. Usually.

I have used this method. I taped the tack down put in the fabric then held the tack with my finger just to make sure. The machine did all the work I just sat there and smiled

I bought a circle maker from Nancy's notions after watching a tv segment using it- cost about $25.....confession....have not used it yet! But, if I get the urge..it will be there. I looked into the real attachment for my machine(BL)...$100.00---no thanks...

This works very well

Draw a circle on freezer paper the finished size you want. Press the shiny side of the paper on the wrong side of the fabric circle and liner. Sew following the edge of the paper. Trim close to seam and turn out. I think you'll be happy with the result.