I've tried the hazelnut I'm both a porter and a brown ale. I give it a C. I wasn't very impressed either time. The flavor was good at bottling, but seemed to morph with conditioning into something less pleasant.
Liquor essences have been around for a long time. We used to get them in brooklyn from a bakery back a long time ago. For sippin whiskey NOT TOO GOOD. For a few heavily flavored or sweetenied cordials or for making liquors to go in mixed flavored drinks like sours or drinks with umbrellas (not highballs or the like) they can pass to some degree.
Add some sugar and or glycerine to vodka dump in the flavoring essence and make sure to age for at least 5 minutes.LOL
From what I've heard, if you want to make a cordial or something to that nature, getting everclear (or insert favorite vodka here) and infusing fruit or berries turns out wonderfully, and probably easier. The other drinks like rum or whisky, I'd personally prefer the local liquor store.
Beer I'll make but liquor I leave to the professionals.
Like I posted before they make liquors that might not pass a panel of "experts" but should be fine for most mixed drinks.
If they are like the ones I have experience with they sometimes needed a few drops of glycerin or other such additives or that may already be in the flavorings. Good Luck.