I saw one in use with what I think was an 11" coil, might have been 12" and it really worked to well, sounding off on tiny, tiny fragments of metal.
Hobbyist who posts on a couple of forums has used the larger coil (3 x 3 I would think) and found it to be deeper than the TF900 (two box) but not much deeper and there was a steep learning curve and much fiddling with timings. Same applies to most of this type of detector though.
I should do a web search and ask for further details. He's not a dealer so the information should be accurate.