we use the Pedi-Paws at hubbies' moms house for our little dogs, it works GREAT, so great that we asked for one for our dogs so we dont have to use theirs haha
they also use it for their dogs, who are a 12 lb chihuahua and a 25 lb pug, both with thicker, black nails. ours are 5 & 7 lb chihuahuas with a mix of brown, white, and black nails which are all pretty little/thin, so it works on all those kinds of dog nails. idk about big thick dog nails.
the only advice i have is when i do it, i touch the nail to the spinning file and pull it back every few seconds because i dont want it to get too hot on their nail, you know how when you get your nails done at a salon and their spinning file sits too long on one spot how it burns really hot? it could be like that so i'm really careful!