It is a bit hard to see the angles from the photos but it looks to me that the brace is just there to keep the spreaders from wobbling. In normal conditions it doesn't look like the loads will be very high on the brace, not compared to the loads on the spreaders. Under high wind conditions there may be whipping causing some load on the brace if the mast starts to pump or if the boat hobby horses. These loads will alternate between compression and tension. I'd be cautious sailing in high winds or in a seaway.