Dark Realm and Vision

The Secret Kingdom (Thicket), the level 523 Realm introduces something new to the game. That realm is a dark realm. What does it mean by a dark ream?

On the world screen, we can typically see a 5x5 grid showing us the areas around us. However, in a dark realm, you can only see the square you are standing on.

Vision is a level 500 skill. It is listed under the defensive tree. The official description :

Lights up dark realms. More skill points allow more vision on the 'Map' screen. (Vision radius increases every 50 levels.

However, the description is not clear on what is the 'initial' vision?
What if there is only 1 point in the skill? Does the vision radius increase?
Here's the deal :
Level 1-49 : Only 1x1 grid is shown.
Level 50-99 : 3x3 grid is shown.
Level 100+ : 5x5 grid is shown.

So, the first question, is level 1-49 even useful?
On undocumented aspect of a dark realm is that your attack is halved.
With vision, that penalty is removed.

What about level 150? Are there any advantage?
With level 150+, you can view 7x7 on the realm map.
It does not affect the world map.
Since most player use fallen sword guide or the wiki for their maps, I'd say level 100 is probably sufficient for most.

In fact, level 1 is probably enough, just to remove the half attack penalty, and any higher levels is more for convenience.