The answer to this question depends on what you want as a free to play player, if you are trying to get as strong as possible the vit pots will be worth it long term, but short term if you miss a character because of 10 pulls a month, that might hurt you

10 pull is definitely more beneficial. Buying vitality won't give you anything it will only speed up the process of grinding.

id only do that if i have the monthly card but if you dont care much about limited characters i guess its fine

If you only buy the 1st vit pot for a month you would have 900 stamina. The same amount of dark crystals would give you 1 limited 10 pull. Which do you think is more valuable?

Is it worth to trade 50 dark crystals for 1 vitality pot every day?