I can't comment much about
GW's sprays as I've not used one for over a decade.
I can say that Halfords offer a 500ml flat black paint that is nigh on identical to chaos black primer spray - comparing the quality, flatness and durability of my sprayed model vs one sprayed at a
GW store by the manager with their brand. (technically one is paint and one is primer.. but this appears to not mean much this particular time, both adhere very well due to solvents in the paint, and both are very black and very flat and high in tooth.)
500ml Halfords matt black costs less than 400ml of
GW chaos black.
I use all Halfords sprays, primer grey white and red, black paint, khaki cammo paint, glossy and matt lacquers.
Nothing wrong with any of them.
Prices are mid range when seeking other suppliers and brands, but cheaper than any hobby brand.
Availability the draw for me, theres a halfords store less than 10 minutes walk away and they serve all my rattle can needs really... its actually closer than the
GW store by about 3 minutes too