Do I want a Primer or Sealer ?
Which one ?

Primer.


Worth going for their "Premier" ?

Usually the better stuff lasts longer.


They also offer in a spray can. Any good for a small area, or just use a
brush ?

The bush might be easier since it's a small area and you don't have to worry
about accidently 'spray canning' something else. The downside is it's
easier to store and be able to reuse the remainder of the can than a tin of
primer.
xxcarol