I have found the Gravitron is great for training your planche. For the longest time I was unable to move from frog-stand to tuck planche according to Coach Sommer's progression. This helped me break that barrier and make further progress.
To be clear, the machine I am describing is an assisted pullup/dip machine with a platform for your knees which is counterweighted and moves up and down. What I did was kneel on the platform facing backwards, away from the machine, using about 40 pounds of assistance. When I was kneeling, the platform moved all the way down near the ground. I put my hands on the two steps that were attached to the machine, and the 40 pounds of assistance was enough that I was now able to hold the tuck planche position with ease. I did sets of pushups in this position, and also in the advanced tuck planche position, and reduced the assistance weight as well.
That was two weeks ago, and with practice I am now able to hold the advanced tuck planche for a second or two, and the tuck planche is even easier. Using the gravitron machine for assistance with planche holds has really helped my ability with this progression.