I use a ninja blender to mix it up by the gallon. It help my digestive system to leave it in the fridge overnight to soak up water, but even then, I find it important to have water in an amount of at least 50% of the amount of Huel I consume. If I forget the water or drink too much Huel before it has soaked enough, it leads to a lot of unpleasant issues.
If I can’t premix, I use a portable battery powered blender that works better than any shaker I have tried, so long as you follow the directions properly. It is called Promixx. The rechargeable one is more powerful, but twice as expensive and results much the same with Huel. The others take AAA batteries. The nice part is you can let it go a little longer and it seems to make it a bit smoother. I add an ice cube and shake it a bit to make it colder. It still doesn’t quite compare to the batch refrigerated overnight, but it is cleaner and better than the shakers I have tried.