The same effect can be done with just a leash. Go to any AKC obedience class, When the dog is on a
sit, the lead can be lifted slightly up to cause a negligible tug on the collar. Sit, tug, sit physically re-enforces
the sit command. Once sit is thoroughly condition in this manner, the dog will resit moving even when a
stronger pull to move him is applied.
Pointing dog trainers use a similar approach to re-enforce "whoa". The pointer is set up with a snug collar and
stiff checkcord. When the dog hits a point the "whoa" command is re-enforced by slightly twisting a very stiff
checkcord transferring a small re-enforcing pressure to the dog's neck via a tight collar. This effect is much
more difficult to consistently reproduce than pushing a button on an e-collar.
If you place an e-collar on a pointing dog there is no question most will jump on that application....especially if
it is a Lab. Even if the Lab's natural point is re-enforced via low levels you will most likely be severely "chastised".
Don't ask me how I know this.
Frankly, when finding out what level would work on sit with Pounce (retriever, not a pointing Lab), I could not
feel it. However, her eyes would blink exactly as a cue every time.
Here is a link to a video with a very young pup where slight tugs on the lead are used to re-enforce the sit command.
"Hillmann Training" with Jim Wegner (YouTube)