Is there a significant difference in flavour between real Mirin and Mirin-like products?
I used hon-mirin exclusively when I lived in Japan, simply because it tasted better. 

My Japanese neighbor was surprised that I could tell the difference, and confessed (somewhat embarrassedly) that she used aji-mirin since her family couldn't tell the difference. 

However, I cannot buy hon-mirin in the US (I'm not 21, and hon-mirin is sold as wine while aji-mirin is cooking wine) so I've been using aji-mirin without detrimental effect.