‘RE’ in the product name of a magnetic stirring bar stands for rare earth. Rare earth stirring bars are usually identified by a (chemically inert) black spot on the stirring bar.
Rare earth magnets provide significantly increased magnetic strength compared to standard magnets – stronger attraction between the stirring bar and the hotplate. They are useful for stirring viscous samples.
Rare earth magnets are also almost completely resistant to demagnetisation, in contrast to standard stirring bars, which lose their magnetism with time and use and so require regular replacement.