It works, but...

... is less effective as a ”witness coat” to show you flaws in the substrate where filler or sanding may be needed.

... in additon....

...a colored coat coat evens out the colors of the materials so the finish color has a more uniform color.  For example if you are using white styrene with red brick sheet, grey and black detail castings, and  brass wire bits.  A colored primer will even out all those colors o the final coat will have the same color across all the materials.

However to answer your question, Dullcoat is basically paint without any pigment in it, so it should work pretty much the same as a primer.

  "is less effective as a

Yeah, a good primer like the Tamiya spray can will show up flaws you didn't know you had. It's almost impossible to pass their test :> ) .....DaveB

Did you scrub the plastic with soap and water and let it dry

before you painted the plastic kit?  Most plastic comes from the manufacturer with some sort of mold parting coating on the plastic.  If you don't get it washed off, even primer won't stick to it.  You shouldn't have that problem with the Campbell kit.

Dullcoat follow-up

Thank you for the input.  I have not washed the plastic, although the thought later crossed my mind.  Neither my Walther's Merchants Row kits nor my Walther's Consolidated Dairy had general problems.  There were some areas where multiple coats might be needed if a "newly painted" look were desired, but otherwise nothing of concern.  (I am looking at general appearance rather than contest quality.). The problem became a PROBLEM with a Bachmann Spectrum kit, where the Testor's acrylic paint actually started to bead, not unlike oil and water.  My artists acrylic, being more like a paste did nod bead, but was not adhereing well.  As the parts were "new in bag", I thought accumulated oils would not be a problem, not considering  any manufacturing chemicals.  I will see if cleaning helps on the yet unpainted parts.  It does appear that a coat of Testor's gray primer is sticking on as unwashed part.

The Campbell kit, being wood, had no paint problems.