A slipper won't interfere with the EBC, they can work together, the slipper will just provide extra slip beyond what the EBC can handle if you really got a significant variation in rear wheel speed vs. engine speed. As noted above, some riders will find that EBC is enough to keep the rear end from squirming and there will be no need for a slipper. For someone racing or Advanced track days, they might still find a slipper is beneficial. That's something that I would save my money on until you see a real need for it, since the slipper will go through clutch plates faster than a non-slipper will.