Yes there's a noticeable difference. Cocktail bitters are a significant variable in the flavour profile of any drink and you can really change a drink dramatically with just a few drops, that's the point of them. D&Co's Orange bitters though? Honestly compared to making orange bitter from scratch to get the specific flavour profile you are after it feels a bit like the D&C guys just went for an easy cop out on how to have a more complex orange bitters. Fee bros is sweeter and far simpler than the other two, angostura is a bit synthetic, Regan's is the pick of the bunch if you had to just go with one for most drinks.
Honestly though the internet is full of opinions. Your cocktail game will improve out of sight once you start trying things side by side. Make the same drink twice and only vary the bitters, see if you can taste the difference, get your friends to sip them too and see if they can taste it. If you can then it's a real thing.