Customer service - You can chat with them live on their site and get real-time advice/recommendations/help with your order. They also actually read the notes you leave with your order. Last order, I insisted upon a freebie flavor and told them to draw a balloon on the receipt if it was ok for me to insist like that. They drew the balloon, a smiley face, and a "happy birthday" for some reason lol.
Shipping - Always incredibly fast. Usually ships the same day I place my order, but if not, always the day after. Gets in the mail to me in about 3 days every time. I've ordered from around 5 other vendors and none of them even got here in twice that time. Never had a leaky/damaged package.
Freebies - If you spend more than 15$ on an order, they throw in a free 15ml bottle of juice. You can insist on what juice you want in the comment section of your order, and even the PG/VG and nic ratios. They will mix it so quickly that they usually hand-write the labels for your freebie to avoid wasting time with printing I assume. This is basically free juice tbh. It's a business model that keeps customers coming back for a new juice, or simply to get a free bottle of a juice they already love.
Options - On their site, you can customize PG/VG ratios, nic %, and flavor shots for every flavor they offer. They also offer a "build your own" section, where you can mix flavors and ratios to create your own juice. Out of the 10 or so I've created, only one of them was awful, and it was my fault (chocolate raspberry... nasty). Again, you can customize the flavor shots and PG/VG ratio for the "build your own" as well.
Flavors - Their flavors are really straight forward and tasty. I've tried multiple more expensive vendors and I can't justify paying so much more and waiting so much longer for a juice thats really not all that different from MBV. This is subjective, obviously, but I haven't had any issues with the tastes of their juice whatsoever, and have been enjoying all of the flavors that I thought I would enjoy.