I had one before I bought an actual frame. It worked quite well for me within my limitations of size of machine (at the time I had a 9 inch throat Janome that worked on it). Also, you still baste your quilt together, then clamp it to the frame. It's a good, inexpensive system. The one I had could do up to a double size quilt.
Another attraction was that the frame could be taken off the table and put against the wall, freeing the table for other purposes.