There is nothing keeping the car from falling off the platform if the hand brake is not put on or if the brakes are being worked on.
Not easy to tell from the photos, but it looks to me as though the car is resting on the beams on it's jacking points. The wooden ramps are only in place to get the car above the beams.
To raise the car evenly would take four people though...
As for the Hi-Lift (Sheepherders Jacks) I only have one (a 5ft, which is too long to carry in the 90, purchased when I owned a 109" SIII). I use it at home occasionally for a quick lift of one corner of the 90 (or more often for pulling stubborn plants out of the garden!
).
