All flavor houses try to imitate flavors to the best of their (or their supplier's) ability, with reasonable profitability in mind. A concentrate is comprised of anything from a few to a whole bunch of compounds, and while each one inches you closer to an authentic flavor, it also increases the cost. It's not so much about quality as it is about bang for the buck. And some manufacturers are probably a bit greedy, I would assume that RND usually stops when the result is just acceptable.

With that in mind, if you compare two concentrates, you'll often find that each interpretation of the flavor brings part of the real thing, but neither quite gets there. So to get closer to an authentic flavor, you can often combine two decent concentrates into a more accurate flavor. For this reason alone, you shouldn't really rule out any brand.

Some brands are better for certain flavors, some brands cater to vapers while others want nothing to do with us, some may contain things that are dangerous to inhale. I would suggest sticking to the well known brands and getting to know their limitations. You should be able to get all the major ones in Germany or import from within EU.

Yes. Flavors can differ greatly between brands. Testing single flavors is alway a good way to get to know them. There are also flavor reviews in this sub.

https://www.reddit.com/r/DIY_eJuice/wiki/index/flavor_reviews

Here is a wonderful resource that has helped me tremendously.

Really good ones are ones that have been around a while, like capella, tfa/tpa, flavors art or FA, inw, flavorah, or etc. Yes it's different, it's as different as food brands at your grocery store or..Lind of like cola ..Pepsi and coca cola make two different varieties of cola.