Dragons need more floor space than height, so at best, if you do buy the screen terrarium, lie it down on it's side, so you have 48"x30" of floor space and 30" of height. The one thing I am concerned about with these cages, is the screen itself. It's a sort of plastic/vinyl and with the heat needed to warm a dragon's basking spot (95-115F) could melt the screen, especially if it gets in contact with either the bulb or hood.
Because it's all screen, the heat will escape constantly, so the only way to maintain temps would be to heat the room the cage is in to 70-75F to minimize heat loss in the cage. Then you can raise a basking spot to the required 100F or there abouts.
The point of claws getting stuck and dragon's loosing toenails won't matter on the dragon's age. The screen is a double woven mesh with various sizes to the openings. It's a consistant pattern but there are small and big holes between the mesh for dragon claws to get caught in.
In the long run you would be better off building your own cage. It is alot cheaper to make it out of wood, whether kiln dried pine or spuce plywood or melamine. You can make a partial screen cage, solid on bottom, sides and back, with screen doors and top. Hardware cloth (1/4" wire mesh) can be used on part or all of the top or having a solid top and mount your light fixtures to the underside of the top.
On more point about the screen cages I didn't like. I have seen the size of screen terrarium you described setup in a petstore. It had a black tree monitor in it, the interior was very dark, even with a basking light and UVB bulb shinning into it. it might be how they had set it up but the cage was gloomy, nothing like the bightness dragons need to thrive. The top was well light but the bottom is dark. Since you can't mount the lights to the cage, you either have them sitting on top which most likely will melt the screen or hanging inside where the dragon could get into contact and burn himself. The black tree monitor didn't look very good either, he had major nose rub damage on his mouth, which was red, swollen and looked painful. I really don't think a dragon, or any sun loving reptile, would do well in these tanks. It may be find for chameleons, who like alot of cover and hides, or nocturnal lizards/snakes.
I have never used these cages myself, though I have considered getting one for my crested geckos but the cost isn't really worth it. Using wood and regular aluminum screening, I can build one for much cheaper. I am no building wiz, so building any sort of cage takes alot of planning to make sure all the measurements are right and to make sure I can build what I want with the limited amount of tools I possess.
-----
PHLdyPayne