Adding milk with alter the calories and macros. I mix mine 1 litre at a time in a blender, divide into 2 500ml portions and leave in the fridge. The consistency becomes much thicker after an hour or two. I actually love the taste of it either way!
My first day was just water & Huel and I was very underwhelmed too. I since add banana & raspberries (or blueberries) and only a few days later now love it !! Just had my Huel lunch on the move right now, off to another meeting on a full stomach
Before you go crazy adding a bunch of stuff to your Huel, ask yourself why you are drinking it. Whether it is for convenience, money savings or weight loss, adding a lot of things to it makes little sense to me. A lot of what I have seen on this subforum is people playing with the idea of making Huel so much more complicated than it needs to be. It is fuel, not gourmet.
While milk definitely works, I think it is fun to keep my Huel vegan. I am a meat eater otherwise, but I like keeping out animal products where it is dead easy (besides, I get rectal fireworks from lactose). Peanut butter is nice also, but incredibly calorific.
I will admit, the first time I had Huel I struggled to finish it. I just found it a little bit nauseating. I got used to it, though. After all, I do not consume Huel for the flavor. The trick is to cool it down as much as possible. Add 4-6 ice cubes!
My second trick to making my Huel actually nice is the mocha flavoring you can buy on the website. It is nice! It says to add half a teaspoon per something something units. I say go big or go home. One topped teaspoon of mocha flavoring in my 3-scoop Huel shake and I am set!