Consider the following:
Nokia Lumia 1520
Screen: 152.4 mm
Height: 162.8 mm
Width: 85.4 mm
Depth: 8.7 mm
Weight: 209 g
Samsung Galaxy Note 3
Screen: 144.3 mm
Height: 151.2 mm
Width: 79.2 mm
Depth: 8.3 mm
Weight: 168 g
Samsung Galaxy Mega 5.8
Screen: 147.3 mm
Height: 162.6 mm
Width: 82.4 mm
Depth: 9.0 mm
Weight: 182 g
Samsung Galaxy Mega 6.3
Screen: 160.0 mm
Height: 167.6 mm
Width: 88.0 mm
Depth: 8.0 mm
Weight: 199 g
With this in mind, the Galaxy Mega 5.8 is roughly the same size as the Lumia 1520. The Lumia 1520 has a larger screen, so it appears that it will have less "wasted space" compared to the Galaxy Mega 5.8.
Nokia Lumia 1520
Screen: 152.4 mm
Height: 162.8 mm
Width: 85.4 mm
Depth: 8.7 mm
Weight: 209 g
Samsung Galaxy Note 3
Screen: 144.3 mm
Height: 151.2 mm
Width: 79.2 mm
Depth: 8.3 mm
Weight: 168 g
Samsung Galaxy Mega 5.8
Screen: 147.3 mm
Height: 162.6 mm
Width: 82.4 mm
Depth: 9.0 mm
Weight: 182 g
Samsung Galaxy Mega 6.3
Screen: 160.0 mm
Height: 167.6 mm
Width: 88.0 mm
Depth: 8.0 mm
Weight: 199 g
With this in mind, the Galaxy Mega 5.8 is roughly the same size as the Lumia 1520. The Lumia 1520 has a larger screen, so it appears that it will have less "wasted space" compared to the Galaxy Mega 5.8.