IMHO, they're a gimmick. Just like the Split Fire and the Bosch +4, and the Accel U-groove.
The Bosch +2 and +4 aren't a gimmick, though they're ill advised for vehicles that aren't specifically designed for that style of spark plug (there are a few high-end European cars that they are OE for).
E3s are so expensive at 3-6 dollars a plug at most places that you won't find many people trying them, myself included. I'm not blowing 12-48 dollars on a product that might not work, I'd rather spend 15-30 on a sure thing.
The Split Fire plugs were proven a gimmick item by most magazines in the early 90s, yet there are diehard fanatical splitfire users the be found.
The Accel U-groove I'm not sure on. I have them in my Chevy pickup, but only because the Accel U-groove header plug and the NGK V-power plug are the only two that will fit with my headers and the Accels fit better (another 1/8-1/4" of clearance depending on the header tube they're under) and last longer (I get about 15,000 to the set of plugs in this truck because I run it slightly rich and the timing slightly retarded to fight detonation on 87 octane gas, I only got 9,600 miles on NGK V-powers)
The NGK V-power plug (another groved-electrode plug) is no joke, I ran those in my 5.0 and followed them with a set of stock Motorcraft, I lost 1.5mpg highway with the Motorcraft plugs.
I run NGK V-powers in my 2.3L stangs with distributors, and Bosch Platinums in any DIS 2.3s I service (the regular single electrode Platinums). Those two plugs seem to be the best by far for 2.3s, followed by Motorcraft, Autolite, or AC Delco (pretty much a preference thing between those three, believe it or not, AC Delcos work pretty well in 2.3s too, but they tend to be about 1-2 dollars more than autolites or motorcraft, and Bosch Platinums or NGKs tend to be cheaper. I'd really recommend a Platinum plug (Bosch or Autolite is usually cheapest and both work well in 2.3s) for the DIS cars because their ignition is essentially a modified version of the "waste-spark" design that wears out copper plugs faster than usual.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
I've been an NGK fan for years. I run them exclusively on just about everything. 5.9L Dodge Ram, 2.3L Stang, and a 2.4L 200hp Mercury Outboard.
I ran Bosch platinums in a DIS 2.3 and didn't care much for them. Prior to that I ran Autolites and the DIS would sharpen center electrode like a pencil after about 20,000 miles. I don't see the same phenomenon in my current dual plug slug with NGK v-power plugs.
The Accel header plugs are a godsend for Chevy heads.
How often should I change the NGK V-PowerPlugs in my Vin M 8 plug DIS 2.3 L engine?
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Originally Posted by b_chandler
I've been an NGK fan for years. I run them exclusively on just about everything. 5.9L Dodge Ram, 2.3L Stang, and a 2.4L 200hp Mercury Outboard.
I ran Bosch platinums in a DIS 2.3 and didn't care much for them. Prior to that I ran Autolites and the DIS would sharpen center electrode like a pencil after about 20,000 miles. I don't see the same phenomenon in my current dual plug slug with NGK v-power plugs.
The Accel header plugs are a godsend for Chevy heads.
talk about serendipity???! I was looking thru 5.0 this am and noted the same advertisement for E3 plugs... anyone with any data on 5.0 use??? They state an 8% power boost (that's pretty substantial in our 200 hp + engines).
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Bad Medicine! 1995 GT, repainted sunfire red with B&B 5.0, forged internals, KB blowzilla,flowzilla, JL CAI, underdrive pulleys, custom burned chip, side exhaust via svo covers and Roush Magna Flows, tremec T-56 with close range gears; 3:73 rearend, drag rear control arms... new front end bushings, rods, etc... Brembro 13 inch Cobra Brakes on front... New interior with interior paint... Wide gunmetal stripes with airbrushed rivets...
More Info: I've looked thru google thus far and most reviews are at best mixed... Seems that the plugs are made in China and quality may be a factor... Given the choice between NGK (proven Japanese) and e3 (Chinese ???) for about the same price, I think I'd go for NGK
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Bad Medicine! 1995 GT, repainted sunfire red with B&B 5.0, forged internals, KB blowzilla,flowzilla, JL CAI, underdrive pulleys, custom burned chip, side exhaust via svo covers and Roush Magna Flows, tremec T-56 with close range gears; 3:73 rearend, drag rear control arms... new front end bushings, rods, etc... Brembro 13 inch Cobra Brakes on front... New interior with interior paint... Wide gunmetal stripes with airbrushed rivets...
They are essintially the same thing as the Bosch +2 and +4 but without the tendancy to foul. In fact there is so much metal on the end of that plug that I don't see how it ever could. I tried them in my Ranger and saw minimal power improvements compared to the motorcraft (though this is only 145hp I'm talking about), but the millege difference was signiffigant. It went from around 23mpg to around 26mpg. And at $6 a plug I expect them to outlast the truck
e3 spark plugs.. 
