I fitted one after a lot of swearing. In the end I pulled the actuator off and then got to the bolts through the engine bay, found it much easier than from under the floor.
I too got about a 1L/100km fuel saving indicated on the dash, but in reality when calculated from fuel fills and the odometer it wasn't quite that much, but still better. It idled and accelerated off the mark better.
After about 8 months just as winter was kicking in, I started getting codes and limp mode on start up, but they would clear on a re-start. After a week of this they wouldn't clear, most of the fault lights came on and a fast idle was the best I could get out of it.
It was tilt tray-ed into the dealer and they did a few days fault finding. As part of that the induction system got stripped and the blanking plate blamed for my woes.
I can't confirm if that was the only issue identified of if any other parts were to blame or changed, but by all accounts there was an induction leak, the finger was firmly pointed at the blanking plate and I got a $650 bill.
I have a week off, I'm out of warranty and a spare car, so I'll be pulling and inspecting the intake manifold in a week or two, so you will get some idea how much crap a BT50 accumulates in 750000km.
Another option is a catch can. The idea is that with oil going into the manifold it gives something for the soot to cling to. Eliminate the oil and it reduces the soot accumulation.