Finished Looks
With a horizontal GPU and side AIO setup within the Cooler Master NR200P, you should naturally go for the solid, vented cover, which will provide the much needed airflow while allowing through a shimmer of light from ARGB components.
Alternatively, there is nothing holding you back from using the glass panel as well, but it doesn't make for good looks, and the AIO will most certainly perform worse as well.
Looking at the top of the NR200P, you can clearly see the two 120 mm SickleFlow fans in the ceiling, and the glow of ARGB elements from within the case. A white LED lights up around the Cooler Master logo shaped power button to let you know your computer is up and running. In the rear, more lighting elements can be seen, while the top-left power connector means access to the motherboard I/O is unobstructed as well.
Finished Looks - Vertical GPU
In a vertical GPU setup with the AIO on the floor of the NR200P, you can clearly see the GPU along with the ML240 Illusion Halo ARGB fans. This makes a lot more sense, but also impacts thermals in some unexpected ways.