this is just a personal opinion but I think they are better for bigger dogs. The grinding part is so big. here are a few experience from friends of mine.
#1- one of my friends had a Pom and she was grinding the nails in front of the dog and it got caught in the fur and kept turning until someone unplugged it. After that the dog had a bald spot right on the front of the body (the chest) and it really hurt him.
#2-this one is an experience from someone that came to petsmart to return it while I was working and they told us what happen to their dog, I do not remember the bread though. But anyways they left the little lid on the pedipaw and put their dogs nail in the little nail hole and I guess it was more powerfull then they expected it to be and the nail slipped under the lid and was caught betweent he lid and the grinding part... it ripped out the nail
.
I guess just from hearing this stories it scared me away from it. I think I am better off using a hand nail filler
Goodluck, some people with more experience will sure give great opinions... I am just scared of it..lol