I'm aware of the failed attempt by an enthusiastic amateur to find Amelia Earhart's wreckage. I'm also aware that the referenced website(s) merely say that the AUV can be fitted with either a single or dual frequency sidescan sonar.
My question is: what frequency is being used in the AF447 search?
I could make an educated guess that the two frequencies are something like 120kHZ and 500kHZ. Therein lies a significant problem. The lower frequency probably lacks the resolution to 'see' a smooth sided object as small as a CVR/DFDR. The higher frequency probably lacks the range to insonify a significant swathe at a reasonable flying height for the AUV over such craggy terrain as the present search site(s).
That's why I ask whether they have deployed a similar sized box onto the seabed to demonstrate what it would look like if insonified by the equipment being used.
Sure, there will be a debris field, but in such a depth it is likely to be quite diffuse and probably enormous. An object as small as a recorder box really needs a methodology verifier.