The oxygen exchange fears with glass tops CAN be for real, especially with big active fish in highly stocked tanks. I'd be leery of any top in tightly closed homes with many residents. But it's not always absolute truth for every tanks. Each tank is different so universal statements often aren't helpful. Also, oxygen levels can be tested if in doubt.
Coral only tanks or tanks with low fish loads are much more resilient with a few caveats. An open topped sump with good turnover can provide some tanks, maybe most, all exchange needed. Depends on volumes of course. Many glass tops have a plastic strip in the rear which can be perforated and provided with vigorous air input via fan or air pump. That alone may do the trick.
They will slow down evaporation, so droplets can form on the underside. This may block a tiny amount of light and diffuse it somewhat. But many of today's lighting systems have so much reserve capacity it may be totally insignificant.
If you like glass tops I'd give it a try as long as many huge rare fish were not put at risk, as long as other methods of air & water mixing can be implemented. If it turns out to be not to your liking, you haven't wasted all that much money. A hybrid glass/mesh top is another possibility if evaporation control is the goal.
Just my opinions based on my observations. I'm not suggesting it for everyone and urge caution if trying it.
