I have a crank scraper and a windage tray on my car
Never been able to show an improvement as a result of it, so I always say if you have the oil pan off it is cheap and one of those things that can't hurt but it is really not worth the effort to do unless you are already in the motor doing work.
The theory behind them is decent. The tiny oil drops hitting the spinning crank take energy away from the rotation, but in reality at under 3000 rpms there just isn't enough stuff splattering around to matter. You might get a 0.01% increase in efficiency at low rpms.