Nothing bad per se, but they are acrylic, so they are prone to scratching. They need to be perfectly level to look good, meaning they should have water spilling over all 4 sides equally, and lastly, you would not be able to cover them, so know that you can lose fish to jumping, as you can with any open top type tank.
Creation Reef has a couple large Zero Edge type tanks they use for their coral sales tanks, if you want to se how it would look/work in person. I think someone there told me they had them built, but that they are not Zero Edge brand.