I would agree. The pet one worked fine for a while but then it wasn't able to hold a charge. I bought a Dremel 120 V multi tool that plugs in and it has worked great for over a year so far. And I can use it for non-nail trimming projects.
Right now I am using the sanding bands that came with the kit and they are 60-grit. They work fine but I think I prefer a slightly finer grit. I think I used the 120-grit with the previous Dremel.
I use the 120v multi tool. It's a 2 speed model and I run it on high. I also use the course(60grit) sanding drum. The faster it cuts the better. When it starts wearing out it takes too long to file the nails and the nail gets hot. The patient does not like hot nails. One drum will do about 10 bullies or 180 nails. I have a battery powered model too but it won't do more than 6-7 bullies at a time and that won't get it when we have nail trimming get togethers.