I find this works best if you soak a cotton pad and leave it on the nail for a few seconds before trying to rub the polish off. It saves a lot of extra rubbing and softens the varnish so that is comes off more easily especially for dark colours and on my toes which always seem to take more effort to get the polish off.
It is acetone based so be very careful not to spill it as it will strip varnish and paint and stain some fabrics. I always make sure I screw the lid on tightly in between tipping it onto soak the cotton pad. Be careful not to lie the cotton pad on anything after using it too as that will also strip stuff off.
It does the job
It smells strong as do all liquid acetone removers