You can merge a model in several ways.
Simple drag the selected items into viewport.
Opened the "Object Place" dialog.
You can clone the merged objects by mouse click.
Hold SHIFT+CTRL and move mouse for free rotation.
For rotate the object by clockwise hold the CTRL and left-click.
For rotate the object by counter clockwise hold the ALT and left-click.
Right-click for stop painting.
Double-click on the item for merge it.
In this case the options for merge will be ignored.
Also you can replace selected objects with objects from file.