I have the 7700 which replaced another used for maybe 16 years before it died. New one is quieter than the first but I was easily able to retrain a dog that hated getting nails clipped into one that tolerated dremeling to the point she told me it was getting uncomfortable by just wiggling a bit rather than all out rebellion. I did this through training using information found on doberdawn's site. That page is about 20 years old now, probably plenty of other good sites on the subject by this time. Don't recall if the sound was an issue with first dogs but it has been fine with current dogs if one approaches this slowly with lots of treats.
I did try out a different brand of pet nail grinder with one of those shields. My 44 pound dog's nails did not fit inside the hole and that grinder was too weak to actually grind nail when I took the shield off so unsure it would help much. Maybe it would help keep long fur out but my experience with cordless grinders is that they stall when hair is wound up and it doesn't hurt the dog or pull out hair. Dog is freaked out though. I do have a dog that would like to bite the sanding head when annoyed so a shield could help with that. He's the only mouthy dog I've had. If your dog leads with the mouth then maybe it would be a good precaution. As for the dust? I grind outside or plan to vacuum after grooming. It is unlikely to catch all the dust anyway.
I did try out a different brand of pet nail grinder with one of those shields. My 44 pound dog's nails did not fit inside the hole and that grinder was too weak to actually grind nail when I took the shield off so unsure it would help much. Maybe it would help keep long fur out but my experience with cordless grinders is that they stall when hair is wound up and it doesn't hurt the dog or pull out hair. Dog is freaked out though. I do have a dog that would like to bite the sanding head when annoyed so a shield could help with that. He's the only mouthy dog I've had. If your dog leads with the mouth then maybe it would be a good precaution. As for the dust? I grind outside or plan to vacuum after grooming. It is unlikely to catch all the dust anyway.