Agree with everything BrotherBob said.
The mix it alone part is especially important because some flavors taste awful alone. That’s completely subjective. You may love most of one vendor’s flavors, bug others may be horrible.
I have 5-6 different brands. Usually, I either like most or dislike most of a brand, but I’m open to trying several. Say, strawberry. I have, gosh, I think 7-8 of them.
Try them alone and you’ll know which has the right taste.
Also, having a few is a good way to fill out a flavor by layering. One is a bit sweet, one a bit too real, one not tangy enough... you can do a lot more with 10% total of three strawberries than you can with a higher percentage of one of them.
I’ll admit I got lucky right out of the gate and mixed some juice that was exactly what I wanted, but I’ve had a lot of fails, too. Still, I’ve saved enough not buying juice that I’m way ahead.
It takes time though, like cooking, lots to learn.