The words of caution against using an ez-out should be magnified. Also, be careful with drill bits, especially with labels saying shatter. You end up using a carbide grinder or EDM ($$ & time)to get a broken ez-out/drill bit and bolt stump removed. You can do the same thing by using a Dremel style tool and a chain saw sharpening bit or carbide bits to grind out the old stud back to the tips of the threads and then use a pick to pull out the bolt thread. It's not as good as an EDM at a machine shop but has kept me from pulling a block twice. And to echo--PB Blaster and tap-tap-tap on the broken piece and around its edge, repeat, until you think it's good enough, then do it again before you get brutal with it. Be cautious and you won't even need a heli-coil, just chase the threads.
One other FWIW- ez-outs are square tapers with one or two cutting edges, extractors are reversed tapered sprirals, and both break without warning, unlike softer steel headbolts. And even my Snap-on ez-outs shatter and break.