The mounts are excellent on these. The acrylic is just thick enough to not bend or be flimsy on a 6"x6", but may be a little less sturdy with the larger sizes.
The only drawback for mine can be remedied though. The Printing options. As of now it seems nothing custom is allowed within the borders of the "mounting area". I had gone back & forth with my proof for me to realize this. Basically you loose the outer 1.5 inches or so, with whatever your design is. Hope this improves.

Good, with one issue...