are these safe and effective on yoyo bearings?
A gallon! Holy Crap! How many throws do you have! 
It should be fine for the bearing, just make sure it’s totally dry before you put it in the throw if it’s a plastic throw.
You can also use fingernail polish remover, which is a lot cheaper, since you don’t have to buy much at a time.
Ummm, go top the hardware store, you can get a pint can. And yes it’s safe and effective.
single quart of mineral spirits was like $10 at Home Depot~
that stuff will dissolve anything~ left a few presumably dead and bad bearing in a contact case for a few hrs and when i came back after forgetting i was cleaning they were great and play awesome. dry them thoroughly and spin it all out but mineral spirits ftw