Whether you choose between a plastic rooftop cargo box or a metal rooftop carrier depends on your view of three things: weather, security and speed.
Your stuff won’t get wet if you use a plastic roof box. A metal rack can’t give you that peace of mind unless you use a waterproof cover.
A plastic box keeps things out of sight. And when something’s out of sight, it’s out of mind.
A plastic box doesn’t require you to tie down your goods. You chuck it in, close the lid and lock.
A metal roof rack pales in all those areas. But a metal roof rack lets you transport stuff quicker.
Swing your things onto the roof, strap down and slip away.
So if you think your strapping skills surpass the loosening skills of the closest thief, by all means get a metal rack like the TG-RK1B906B.