Go for it if you have a good trainer to work with you and the filly.
I think the Gunners are very trainable, but like most really 'feely' super light horses, they can easily be really messed up. They are not as 'forgiving' as some horses, but then those horses do not have as much ability either.
I think a horse's bottom side is really important also. What is this one's dam's side?
I asked Tim McQuay a few years ago just how he compensated or what he did different when riding the deaf horses and he said he did absolutely NOTHING different. He said they are so sensitive, that they learn his every tiny move. I specifically asked if he still said "Whoa!" and still kissed or smooched to them and he said he did the same as if they could hear it and they responded just like his other horses do.