There’s a much better sources imo that are cleaner and more abundant than humans, it’s really easy and you never get resistance or backlash.
Other people are full of imbalances, disease, emotional upsets and embedded trauma that you have to learn to filter out and heal. So it’s worth learning how to fix issues before getting them.
Some people will also sense your attack and retaliate, causing backlash. And also many people are infected with astral parasites that will use the connection to hop to you if you don’t know how to stop them.
Basically the vampirism fad is an advanced energy working practice that can be very unhealthy and damaging done wrong. I suggest starting with the above exercise and learn to take from neutral sources without issues, and work on your protections and ability to sense issues, before graduating to humans.
No entities are needed for this at all. Practice and your own system will start to cultivate qi as a habit.
But you should be present and keep an eye on it. You can have to much of a good thing and make yourself sick. In qigong having too much qi too fast flowing in the wrong paths is called Rebellious qi and it can give you a heart attack. Do not mess with this until you understand it and your own body better. Do energy working exercises to learn to know your system and it’s limits.
Then compare with a servitor doing a night of cultivating and make sure to program the servitor to stop before you get rebellious qi. (Though, you won’t get rebellious qi much from humans as they are very poor sources compared to the cosmos, but they are very dirty so, still not recommended)