It mixes fine and is very effective I think. I use it regularly and always have a small (screw-top) jar on the bench.
Not sure what ATF I have, just whatever red stuff the local car parts shop sold me years back.
Acetone comes by the litre plastic bottle here pretty cheap in any supermarket - also find it useful as a paint thinner for some types that don't do white spirit, tho' that's probably all 'wrong' for reasons of chemistry I don't know about.