Working negatives is one of the best ways to develop the strength, control, and technique for the press to handstand and eventually stalder press.
Here are a couple things to think about when practicing this exercise:

-Control the entire movement and try to keep the descent as smooth as possible. There should not be any moments of acceleration or falling.
-The longer you can maintain a vertical line through the shoulders and hips, the more mechanically efficient the movement will be. Try to drive the legs as low as possible while striving to keep the hips high and arms vertical.
-Don't forget to round your back after you hit your max hip compression to allow your body to compress further.
-Try not to let the shoulders go forward until after the legs pass the arms. Flexibility will be a factor here, but a bit part of it is also fighting hard to push down with the shoulders. Letting the shoulders dip forward too soon results in a much heavier and less controlled movement.
-It is important to let your shoulders go forward during the transition to straddle-L portion of the movement though, otherwise there is a good chance you will fall on your bum.

Personal note: this is my first time doing stalder negatives on floor since my wrist injury. Not my best work by any means but it's good to be getting over my compensation patterns and knowing the wrist can handle some forward loading again.