I have the relatively Inexpensive one that is made for Nancy's notions. it's generic and fits on any machine. Instead of screwing into a hole on the bed of the machine like the ones made for specific brand machines you use an adhesive tape to stick it down. Takes a little more fiddling around to get it positioned right, but it works very well and is a cost effective alternative to the ones made by individual manufacturers to fit their specific machines. I've used it on my Brother PC420PRW (which is one of the machines that Brother decided not to make a circular attachment for). I found it easy to use once I learned how to get it properly aligned and I like the fact that I can use it on all all 3 of my Brother machines as well as on my 3 vintage machines (Kenmore, white and singer featherweight).
Rob