DIY L-AA serums, yay or nay?

It’s seems to be nearly impossible to buy a vit c serum in Spain that’s not either:

-Skinceutical’s 

-Fragance or citrus oils free (they don’t agree with my skin)

-Shipped overseas. I imagine since L-AA is already unstable enough+3 week shipping times+whatever time the lovely people at Spanish customs decide to keep the package does not ensure a fresh serum at my door.

Do you think that with this variable, and being L-AA so unstable, DIY in this case sounds sensible? I’m asking before I give up searching for an option. r/DIYBeauty suggests this:

Would I be doing myself more harm than good? Bear in mind that I can cook a paella (so skills for a lot of alchemic steps in check) but I’m also pretty clumsy.

I’d gladly xpost in Chemist’s Corner but I feel I would be completely out of my depth there.