Perfect fit on our homemade 4'x4' raised bed.  Zippers move well and cover comes with ties to attach to the frame.  Assembly was quick and easy. 
I wish it had ties on the bottom of the cover on the sides of the square, they rustle in the breeze and open up a small gap that lets warm air escape.  That said it is outperforming the low tunnels I built and being able to see the plants through the clear vinyl cover is very nice as well.  I've ordered a second for our other raised bed, the jalapeno peppers and string beans inside are doing well despite cold October nights here in New York.