It's not a problem for normal winching with one winch operator on the skids and the winchman/casualty on the wire but, as I understand it, if you want 2 people on the skids (instructor and student) and someone on the wire, the door area is very crowded and the lateral C of G is out of limits - let alone trying to stay OEI in the hover for the training.
Operations fine but HHO training I am led to believe it isn't suitable for.