Yes, you can mix and match them, the macros on the different flavors are pretty close – within a few percent of each other. It’s a really good way to liven things up a bit. If you have the ability, I usually suggest getting several different flavors so you can pull from all of them at the same time.
I mix up 6 meals at a time in a big pitcher, then I mix up 6 more and it all goes into the fridge for my wife and I. Usually I’ll do 2 different flavors (yesterday it was chocolate and banana). For that matter a couple of the bottles I filled up to the 8 ounce line with banana and then added 8 ounces of chocolate.