I ordered some of the Nicotine River "proprietary" flavors, they arrive today. I was a bit interested in some of them. Most vape stores I've been in where I've asked about flavorings, they say what company they use and in all cases, they've been flavorings that have been equally as readily available to DIY-ers.
I'd say the way they use them may be different-- there is no way I'm sweetening at 5% and mixing total flavorings at 20%. That's just overkill in my opinion, and I prefer to use way less flavoring in my mixes. That is the nice thing about DIY, you can really experiment with what works for you. I started out rather minimalist in my flavorings, and have reluctantly purchased a sweetener and some known sweeter flavorings, but I still imagine I'm going to be in the 3--6 or 7% flavoring AT MOST, and less than 1% on sweeteners.....
Anna