Not sure since I have heard horror stories about shanks breaking on some boxes or the shanks actually bending the box frame because of too much load and resistance. I guess it depends what you are trying to do. I bought a "Woods" box blade because Woods does not put their shanks/rippers through the frame bar and the steel is significantly thicker than most of the other box blades. They weld the shanks on the back of the frame bar for more strength and less chance of serious structural damage.
You gets what you pay for: I bought a cheap used one a while back. Last summer I bent it up when the rippers on one side caught roots. I also have a mostly worn out Gannon (now owned by Woods). It is too narrow, and needs some work, so I bought the cheap one for the meantime. It did the job, but I knew when I bought it that it was light duty.