DISCLAIMER--I do not work for the airlines or government--I just simply know how to research...here are the facts (paraphrased or directly quoted) as I have found them on the internet..
And to answer your question....So with due respect to the flight attendants--according to the FAA web-site they have been reporting incorrect information....
2380-A "During the cruise portion of the flight, however, there is no regulatory prohibition regarding the use of any type of child restraint, including those that are prohibited from use during ground movement, takeoff, and landing."
(The Baby B'Air according to all ads for it indicate it is FAA approved for inflight which goes a step above this statement--www.faa.org lists nothing specifically to indicate otherwise--and since truth in advertising is paramount--one can only draw the conclusion that the ads are accurate and correct).
Children under 2 can be lap babies--but it is recommended to use an FAA approved car seat (defined as well on this site). But for those who can't or choose not to...
According to 2379-F Harnesses are only not recommended for take-off, landing, and movement on the service (mentions nothing about seat belt signs in flight--which are only on when there is turbulence, or the possibility of turbulence (or captain has any other reason to illuminate it). The belly belts I described in my previous post that are used by foreign airlines are not recommended under the same conditions--and thus implied to be okay during in-flight (though British Airways requires them for take-off and landing--must be their gov requirements).
Children who can legally occupy a booster seat...can safely occupy an aircraft seat utilizing just the lap belt. (2379) (and since the boosters are backless, they are not approved for use on the aircraft anyway).
Also in further reading (it is a long document)...no one under the age of 18 can be refused to ride in a CSR as long as it is properly labeled , the child is of the appropriate weight limit and is properly secured (2379-K) [Note that this does not include backless boosters which are not permitted.]
Hopefully this clears up confusion...refer the faa web-site for additional info.
http://www.faa.gov/avr/afs/faa/8400/8400_vol3/3_016_06.pdf
We are all entitled to our opinion--but must remember that their is information out there to support some opinions--such as safety and regulations. If you think something is unsafe--we all want to know about it, just let us know where you found out so that it is fact-based and not rumour-based.
BACK TO THE FLIGHT ATTENDANTS...
the only thing I can think of is they mis-interpreted the next regulation in the document...
2380-B "There is also no regulatory requirement that an air carrier permit the use of 'non-approved' CRS [car seats] during the cruise portion of flight. If an air carrier decides to implement an operational policy that is not inconsistent with the regulations, they have the operational flexibility to do so." So as long as the car seat is FAA approved (as that lovely sit 'n stroll car seat...) then you are permitted to use it.
www.babybair.com has this to say in regards to refusal of use..
What if the flight attendant is not familiar with the Baby BâAir?
If any parent has a problem using the Baby BâAir during flight, they may return the vest directly to Baby Bâair for a refund by providing the airline* and flight information (flight number, date, departure city and final destination). This enables us to follow up with the FAA and the airline.
So my guess is if the airline these flight attendants work for are not allowing passengers to use these devices--the passengers should have been able to contact BabyBair directly so that they can interact with the airline and get it resolved b/c it is supposed to be allowed.
Always check with the airlines about what you can and cannot use and do not hesitate to call it into question against the facts of what the FAA requires and doesn't require.
And for the record--we fly in July to Indiana--DD4 will be in her car seat (we will need it for the weekend) and DD21 months will have her's packed in it's case and checked (and I am now seriously looking at this harness--don't own it yet--just reporting the facts of research).
Safe travel everyone!