But it certainly helps.
The non-scale model of a Garmallis '3 step carrier' model (seen in the original 'Space Battleship Yamato' series) that came as a extra in one of my UN cosmo navy sets is finished and ready to be varnished. Once again because I expect this model to be handled a bit I'm going with a gloss varnish.
I had a bit of a disaster when I under coated the model, the black undercoat split and crazed. I thought it might be something to do with the temperature as I had a couple of problems previously, but this model was undercoated on a warm day and the undercoat still split so that paint has gone in the bin. Currently I'm using a brush and army painter black and the problems have gone (no problems with the destroyers seen in the rear of the image).
My son has brought himself a couple of spray tins of army painter primer, black and red to paint his space marines and he's had no problems so far with that. So once I'm back to the larger (or larger number of) models/miniatures I may buy some myself.