I have had Geoff the grinderman in a few times and he uses a serious bit of kit with a V-twin motor and it has broken a couple of times (teeth, and belt etc) because they (and you) take a right hammering. If your 8 stumps are a reasonable size or hard wood or just difficult shape etc then it will take you days with a toy grinder from a hire shop. Its not just the stump it also any horizontal roots.
Depends on why you want to remove them, if they’re in a lawn, not too big (six inch or so) and you want to grass over them and, a small hired one will probably suffice. However, if you want to remove completely anything substantial then a larger piece of kit might be needed. Our work one is a v-twin, drinks petrol and blunts teeth for fun.