https://www.tiktok.com/@tilta_global/video/7250381959497649450

I'm going to attempt to replicate ...with grips on monitor ...for my wife.
Me too, but she does most of the filming ...well, the tripod really, but anyway.

Has anyone done it?  Things to consider?  I see youtuber Bestboy Adam did it.

I've done it. My build was inspired from Bestboy Adam's. So I'm not attaching the 4d Body by the top handle but via an Arca Swiss Plate screwed to the cameras bottom. This way, I feel that it balances better.
There is a problem though using it in underslung mode as displayed in the screen grab you posted - if you are using the LIDAR at the same time, it will contact the gimbal's frame because there is not enough top cleareance. One solution is to remove the LIDAR mount from the lens mount (two screws, can be reattached later) and fix the LIDAR to the lens via a rubber band.
But even with this hack, you can't achieve full underslung mode.Also, I had to add a counterweight to the flex unit because the 4D's main body is way to heavy to balance properly otherwise. This will be even worse if you use the top handle for attachment and thus increase the distance from the post's fulchrum point.
Another option is to attach the 4D's main body to the backside of the float's harness belt and use something different as counterweight on the float pole's bottom end. But then you have cables running from the post to the belt which will disturb balance. But this is a quite nice solution if you are using the Manfrotto Quick Release Plate Adapter together with the float system and don't use the post.

crispinus Posted at 9-12 22:54
I've done it. My build was inspired from Bestboy Adam's. So I'm not attaching the 4d Body by the top handle but via an Arca Swiss Plate screwed to the cameras bottom. This way, I feel that it balances better.
There is a problem though using it in underslung mode as displayed in the screen grab you posted - if you are using the LIDAR at the same time, it will contact the gimbal's frame because there is not enough top cleareance. One solution is to remove the LIDAR mount from the lens mount (two screws, can be reattached later) and fix the LIDAR to the lens via a rubber band.
But even with this hack, you can't achieve full underslung mode.Also, I had to add a counterweight to the flex unit because the 4D's main body is way to heavy to balance properly otherwise. This will be even worse if you use the top handle for attachment and thus increase the distance from the post's fulchrum point.

I saw the Bestboy Adam video as well.  Definitely want to do post, making it a mobile job for low to high shots.  It'll be here in a week, we'll see.

Impressive setup!