That product should not be used for budgies. Budgies are Psittacines (hooked billed parrots) which do NOT need grit. Psittacines shell their seeds before they eat them, and therefore do not need grit to digest their food.
When a budgie is eating a healthy diet consisting of pellets, a high quality seed mix, and vegetables and have both cuttlebones and mineral blocks, they should not require additional vitamins.
Chickens are Fowls. More than half the world's unique bird species, including all the classic songbirds, sparrows, and finches are Passerines.
With regard to the water soluble vitamins, I would first ask you what diet your budgies are eating.
When a budgie is eating a healthy diet consisting of pellets, a high quality seed mix, and vegetables and have both cuttlebones and mineral blocks, they generally should not require additional vitamins.
The key to a healthy diet for budgies is much the same as it is for humans and other animals. You are best to serve foods in moderation
I would recommend you cut back on feeding spinach to once or twice a week.
Spinach and Parsley contain oxalic acid which binds to calcium, blocks the absorption of calcium and puts stress on the kidneys.
Too much oxalic acid can also cause poor blood clotting and convulsions in birds.
Other green leafy vegetables you can offer include:
fresh beet greens
fresh mustard greens
fresh turnip greens
chickweed and dandelion leaves (ensure they have not been chemically treated)
Are you able to find pellets in your country?
Cuttlebones provide the calcium budgies need.
Since you are unable to find cuttlebones and mineral blocks (I'm assuming ordering products on-line is out of the question in your location) by all means go ahead and use the water soluble vitamins.
I suggest you put just a scant 1/8 teaspoon of the mixture in a liter of water for the budgies.
Please be sure to change the water daily.
Thank you for providing us with the background information about your country.
So many times, those of us in the US, Australia, England, etc., forget that not everyone has access to the many varieties of products and supplies we often take for granted.