As far as using Experimental at a control tower I was told by the FAA center Atlanta and Memphis, that they only require the word experimental on an unfamiliar experimental aircraft that "your RV is a common aircraft and in the database and need not use experimental."
It doesn't really matter what they say they do or don't require.
Your operating limitations are what state the requirement that on initial call to an FAA control tower, you identify yourself as experimental.
It is not a requirement when contacting enroute center or approach/departure control facilities, regardless of what they say they want or whether you are a common experimental or not.