For most of us that use ecollars, it's not a either or. A whistle carries farther than our voice, so we train to both.
As far as going back to the ecollar. You would need to do it very slowly, due to past experience. In fact I would not even turn it on for the first 2-3 weeks he wore it. Vizslas have a mind like a elephant, and he may, or may not be able to overcome it.
In the mean time you can still use a check cord, and a whistle to work on recall.
If, and when you try to reintroduce the ecollar, he will already know the whistle command.
Not all those who wander are lost.
Life is just a leap of faith.
Spread your arms and hold your breath and always trust your cape.
Two things define you. Your patience when you have nothing, and your attitude when you have everything.