I use it regularly. I like it much better than the old cycle parking — with the old cycle parking it was simply never possible to get a space (at least at the times when I arrived) and so I always had to wander around the car park looking for some bit of fence to attach the bike to. No doubt the new parking will fill up eventually, but as yet, I haven't even had to go to the top floor to find a space.
The new parking is also covered from the rain, and your bike doesn't get all sticky from the lime trees. I take your point about it feeling unsafe but at least as long as the trains are running there always seem to be lots of people parking and retrieving their bikes.
I'm able-bodied, so I always use the upper tier of racks (leaving the lower tier for people who might not be able to lift their bikes). On the upper tier, there are two loops for locking, so I bring two locks and attach the rear wheel and triangle to one and the front wheel and frame to the other. (But maybe this is overkill and no-one would want to steal my crappy bike anyway.)