In a damp climate they have a tendency to rust quite rapidly and get stiff. I have to remove mine from the bumper, clean and greased them within a couple months of new. Once done they work quite well. It's been over two years and they're still very workable.
To deploy them pull towards the center of the trailer until they release. Once in the down position push down on the lever that towards the outside of the trailer. The foot should drop to the ground.
I don't like the video because I see no need to jack the trailer with them. It looks to me like a good way to tweak the frame.
I think the best way to set up and level the trailer is as follows;
First level the trailer side to side with either blocks under the wheels or using a BAL leveler, (BAL leveler my preference).
If you're not using a BAL leveler then make sure you chock the wheels, then unhitch.
Once unhitched lower the front the trailer with the tongue jack to somewhere between 1/2 bubble and 1 bubble off level with tongue low. (NOTE: Will need some kind of level for this process)
Deploy the rear stabilizers with the feet against the ground or blocks.
Raise the tongue with tongue jack to level.
All done, no fussing with jacking bar on the stabilizers, no tweaking of the frame.
Byron & Anne enjoying the everyday Saturday thing.