Not every vendor is for everybody. I know it seems like the phrase is overused here, but taste really IS subjective. With that said, when I first tried MBV, I wasn't overly impressed either. I didn't note a weird aftertaste, but the 3 or 4 flavors I tried were "meh" and I found a better version at a different vendor. I had sadly chalked them up to not being for me, despite the great prices and stellar CS. Then a friend (who loves and swears by MBV exclusively) opened up a local shop so a bunch of us turned out for his opening day. For the heck of it while waiting my turn at the purchase counter, I tried some of the flavors at his juice bar. Some of them blew me away! So to make a long story short, I am now in love with about 15 MBV flavors that I will religiously order when I run out. (I'm a juice nut with a TON of flavors.) Are they my only vendor? Nope ... I have about 5 more that I order the same amount from religiously as well, but I'm in love with the flavors I do order.
As for the aftertaste, as I said, I didn't get that with MBV at all. I know what you're talking about though, as I DID get it from Alice in Vapeland at first, which went away completely with steeping and I now love several of their flavors; and also got it from another vendor I won't name, as that taste NEVER went away with several weeks of steeping. *shudder*
Oh, and if I matters, I use 50/50 exclusively if given a ratio choice.