Was talking to someone up at Selland Auto Transport last week, and he said that the screw units they have are doing quite well. (I think they have one from Boydstun and one from Cottrell.)
He said that the initial preventive maintenance to the screws was "a bit intensive", but that after the first couple months or so, it isn't too bad. The screw gear requires a special gear oil to lubricate the gear that raises and lowers the decks of the car hauler trailer.
I spoke with someone from Toyota Logistics, and he said that one of the main benefits of this type of trailer is much-impoved driver safety. By lowering the top positions down, the cars can be tied-down at (more or less) ground level. When this is complete, the positions are raised, and then the cars that go on the bottom deck can be loaded and tied down.
Seems to me there would also be pretty good improvement in terms of less damage to the cars-- less pillars for doors to smack!
Not sure how they weigh out, but the Toyota trailers running all straps for the tie-down system must save quite a bit of weight over cluster chains!
I'll be posting some pictures from Boydstun after I go up there later this week.