The Problem(s) with Shock Collars
First off, calling a shock collar an e-collar is nonsense. It's a redirection or spin on what the thing actually does; It shocks the dog with electricity. Big shock, small shock, doesn't matter, it's the same thing.
The nature of that itself is counter intuitive to the dog understanding what the hell is going on. It's invisible, they can't tell where it came from or what it was-like getting hit by lightning, you can't see it coming, it has no connection to anything in the immediate vicinity and it's completely random in it's perception of the one being struck.
Secondly, the timing of the shock, or ok, "stimulation" is what's most important. In real training, we call this "the correction", and it can refer to the shock, a word and tone of voice, or a tug on a leash connected to various types of collar or equipment attached to the dog. So, it doesn't matter whether you're pushing a button, yanking on a leash or uttering a voice delivered "stimulation" that is, by it's nature, unpleasant in some degree to the one receiving it-your beloved pet. In my experience this is the crux of the issue, NOT what you are using, be it shock, collar, voice or a pillow tossed across the room that makes impact at a given moment.
Humans, frankly, aren't very good at this and it takes practice and certain hand/eye coordination and timing to get it right and have it be effective.
So, if you combine the common inaccuracy of human timing with an invisible, untraceable "stimulous" you've doubly handicapped the poor animal trying to figure out what's going on in getting an accurate perception of the situation. The leash, the voice, the pillow-all have a connection to something real and easily related to and perceived in the immediate area and environment they can figure out.
Sure, eventually, the dog will figure out that you're now Thor God of Thunder and Lightning, but not as quickly or easily and producing much more stress and confusion in the process for them.
Add to this the also very human quality of error in the intensity setting of the device, the inherent malfunction probability in all electronics (do you like your cell phone ALL the time?) and the need to take the device off and put it on your dog while you change batteries, charge it or are not using it and you have a multi-fold argument for not using this very troubling device at all.
I've heard people who are proponents of shock collars compare the sensation to a "tap on the shoulder", a "tingle" or other such terms that infer a mildness that may very well compare at very low settings. But, however, mistake the directions or fumble with the DIP switch setting for intensity on the thing and you can deliver a shock that will literally take a full grown man off his feet in pain and sensation. At it's highest setting a well made shock collar is equivalent to just below a thing police call a TASER or a STUN GUN-though the frequency of modulation of the electricity is different so as not to interfere with the neurological system. In a self defense application for individuals or law enforcement the current is set to the same frequency as the human (or canine) central nervous system and causes muscle spasm and paralysis. Watch video of someone getting "tased" and see if this is what you think is necessary to get your dog to come when he's called.
The hypocrisy of then terming this in advertising as "more humane" is comical, and I don't mean ha ha funny, I mean like Dante's Inferno type "comedy".
Then call him "your best friend".