I used some at bottling with an ale not long ago. I used 1/2 teaspoon in a few bottles and 1 teaspoon in a few others. The bottles were 750 ml. I believe the equivalent for the full teaspoon bottles would be close to 4 ounces for a 5 gallon batch. The flavor was not overbearing at all in either, but you could definitely taste it.
I might do it again at some point with the rest of the bottle I have.
I don't know if this helps, but it's my experience with oak essence.