These paints are formulated to grab onto and seal raw surfaces such as untreated timber, brick, fibre cement sheeting, and metal. They provide a barrier against moisture, and have excellent coverage.
Circle Paints is given very little white primer by trade painters because leftover primer can be used for their next job. So if cost is important to you, read on to consider whether you really need primer for your job, or whether you can skip it and save money.
If your surface to be painted may have moisture coming from behind (such as moisture wicking through mortar in brick or a damp stains through a ceiling), primer is definitely required.
If your surface is unlikely to have moisture issues, it may not be necessary to use undercoat. You will use less top coat paint if you use an undercoat first, but you will still need two coats of the top coat to get an even finish.
Like primers, good quality paints like Dulux Weathershield are also formulated for use on raw unprimed surfaces and will generally provide solid cover with two coats, even on an unprimed surface. So the undercoat may serve no purpose and the total job cost will be lower if you skip the undercoat.