Dear Yogis
There is also like on halasana a discussion on Matsyasana because it also can destroy parts of the cervical spine.
Some love it, some gave up teaching it.
So I thing there is also a need to dicuss it and I?m persanlly keen if anyone of you knows about possible safty supports for this asana.
All the best
Lars
I have an exaggerated cervical curve since birth. Family heritage. Too much Sarvangasana in a former life. 
Matsayanasana brings great relief. Very good pose for toning the back muscles.
There is not much bodyweight on the neck. I’d say it is much safer than Halasana.
Forgot the most important part … back muscles should be fully contracted to stabilize the spine. Because of this I perform it as a strenght pose, for the lenght of only six breaths, to a maximum of 12 in a good day.
There must be no ambition to force the head all the way back, I’d say only 85-90 % of the maximum mobility of the neck should be used. It is more important to have the whole spine fixed and stable, from lumbar area to the uppermost vertebrae, using a the strenght of the back muscles. Bend back just to the comfortable level, then muscle-lock. Keep it a few breaths, slowly release the muscles, put the weight more on the elbows, and get back to prone position.