What is so special about equal length arms?
 

I was looking at the box of my B4 and I saw this mentioned like some kind of advantage /special feature.Why equal length arms are important?

Anyone?

Do you have a picture of this?
Where did you see this on your box?

The B4 does have "equal length arms". There is no specific benefit, but better to have arms of similar lengths than ones of greatly different lengths because it will keep the front and rear geometry more consistent.

Equal arms
 

Having equal length arms means the camber does not change with suspension movement.
Shorter top arms gives increased camber on bump and longer top arms give reducing camber on bump.
Its up to you which is best.
On roll things get more complicated but again its how it fits with the track and your driving.
Good luck

No it is not about camber gain , it is about hingepin to hingepin dimension. Unfortunately i cannot grasp how it leads to more consistent handling by itself

Yes they mean front and rear arms are equal in length (not arm vs camberlink).

Losi xx had very short rear arms, which make the rear end so stable the car wouldn't steer anymore.