Though many yoga schools consider this as the preparatory pose for headstand, I believe this is tougher than a headstand if you decide to stay longer in it. The headstand itself is far lighter than this pose. This is because your body is still close to gravity and therefore its power and drag is more felt.
Here is why this pose is tougher and demands more strength than the headstand:
* It is closer to gravity, so the drag on it is more
* The pressure on the neck is continuous, unlike in the headstand where after the initial pressure the whole body weight shifts to the shoulder.
* The tripod in a basic or even the unsupported headstand is more stable while in this pose, even in its basic variation, it is very unstable, and the entire instability of this pose shifts into neck.
How to avoid injuries in this pose:
* Practice unsupported headstand before trying this.
* Prepare the neck through regular leg raises, with the head lifted up (including in the suptapawanmuktasana) to strengthen the neck.
Do not try if having
* Neck problems
* Weak balance (strengthen it in standing poses first)
* High blood pressure/heart problems