[Perfectlap]

it depends on the age of the paint. If its a newer car that is garage kept a paint cleaner might be overkill. And remember you only want to rub on the paint a little as necessary year round. People forget how soft the German clear coats are. They are actually banned here in the USA because of their chemicals. So if you have your car repaired by a Body Shop they are not using the same materials. The base coat might be the same.

If the car is kept outside and is a few years old you should use a paint cleaner like P21S or 1Z (looks like a speedstick deodarant).
Don't know about other brands but you can't use Klasse Sealant Glaze without first using their cleaner/polish: Klasse All in One. They are formulated to bond together or something.
Many people use Meguiar's ScratchX before proceeding to the cleaner and sealant. Works well but requires lots of elbow grease. (speed, never pressure).
A great job for the Porter Cable orbital polisher.