I've never tried them but I do take the time to Index my conventional NGK plugs.
I have done this for years and believe there is a benefit to unshrouding the spark and promoting better flame propagation throughout the burn, which is quite similar to what E3 plugs are trying to accomplish.
I DO NOT use washers but rather swap plugs until I find ones that work. It sounds like a pita, but with a 3/8 cordless ratchet, it goes rather quick. I use a hand ratchet/torque wrench for final tightening, not the cordless ratchet.
If the electrode points up (toward the valve covers) in an arc between 10 and 2 o'clock, call it good. While not ideal, even 3 or 9 o'clock is better than pointing the electrode down (into a dead area of the combustion chamber).
Some combustion chambers will benefit from this more than others.