RebelAir
Air-Valve Autobot!
Realism is in the eye of the beholder, for me personally scratching looks fantastic from a distance but up close can look horrid, traditionally hair was painted into the layering sequence and like any technique in airbrushing has been tweaked to suit different applications and sometimes that tweak takes over in every other aspect, erasing and scratching have been around in all artforms for a very long time but have become much more prevalent recently than previous techniques maybe used in a similar need, learning how to create negative as well as positive space is any visual art and those who only erase are hurting themselves and those who only paint hurt themselves, learn both, but saying that I feel painted hair looks more natural and thus realistic, but for some perhaps less photo like that scratching or erasing can achieve, soft erasing is hard to do on metal but not impossible and various techniques and chemicals can remove any amount paint you want; often on auto work, a cotton earbud and thinners are my best friend..LOL and if wanting to save myself time and cost, it is a method I will use but always prefer to paint hair, just takes longer to get looking right but both methods can get to the same end point and often you'll want to use both if going for a strong realistic look..Good luck..