so you want to buy an s7 then?
if you are looking to replace burnt out blades you may want to specify which batch number blades you are looking for.
3 would be a entire S7. So if your looking good blades, might as-well just buy a S7.
He also might be looking to have blades to plug into IO board that has more then 3 spots. But since buying 3... again just getting a entire unit makes the most sense.