Interesting...so if I order cherry flavoring from one vendor and it tastes like a diet soda - serious yuck LOL - will it taste like a diet soda regardless of who I buy it from?
There is a difference in the same flavor from different manufacturers. A cherry from one might taste different from another. So it is a real gamble buying pre-made juices. They might mix from one or two or more manufacturers to get their special juice.
Buying the flavors for DIY means testing one against the other and determining your own favorite.
So, the answer to will the diet soda taste still be there is not easy to say.
I use flavors that are sweet for my juices instead of the artificial sweetners. I love the cotton candy and the marshmellow, and caramel for that. There are many others I also use.