I think that you can't use this contraption for anything.
The reason is that every car jack I've ever used and own all have a lable stating that they are for lifting the vehicle to a safe height to insert permenant jacks only and the vehicle should not be worked on whilst supported only by the trolley jack.
Unless this lift has some way of fixing it in position after it is raised by the trolley jack I wouldn't want to use it.
I agree with you, I had not looked closely enough to notice that this bench did not have a locking mechanism to lock in place once it is at the required height.
If you look at the photos then you'll see it does have a locking mechanism.
Don't understand why people are getting so childish about this, if you're not interested then just laugh/tut at it & move on, why bother plaguing the guy with silly questions? Are your lives really so sad & empty?
OK, it looks a bit rusty, but from the pics that's just superficial, underneath it seems solid enough, it's a high starting price but I doubt you'll get a hydraulic bench any cheaper, think my Machine Mart one cost me ~ £300 about 10 years back.