My husband made me one of these "fan" frames by looking at the picture (he was a union carpenter by trade.)
I have used it several times. I haven't had any "sagging" problems. I tend to have mine in too tight and the 1 x 2 will "bow" slightly. I've used it to simply do straight line quilting and cross hatching. I like that it doesn't take up a lot of room depth-wise. The angle at which the quilt lies works well for me.
The last time I used this frame I used an office chair so that I could easily slide side to side as my quilting progressed. I also butted the frame up next to the buffet in the dining room so that I could put a desk lamp (with an extendable arm on it) on the buffet. Was able to move the lamp up & down the buffet for perfect lighting.