The key ingredients in the recovery drink that Huel does not contain are the electrolytes; every vitamin and mineral is contained in Huel as well as the protein and carbohydrate, albeit not as concentrated. Instead of splashing out on a supplement like SiS, maybe it would be worth sourcing the electrolytes and adding them to your Huel meal. There are plenty of powders that offer electrolytes without the protein, carbs and VM, this may be more cost effective?
Let us know how you get along.