Websocket “subscribe_entities” syntax

I am using a mcu with very limited memory for Websocket access to home assistant. Using “get_states” is a no-go, because of memory limitations. Now I saw, that the “subscribe_entities” function makes it possible to subscribe to only one enitity. Very good function for small MCUs. The overhead is very limited and there are no memory problems. But the function is not mentioned in the websocket API docs. Will it stay or is it possible, that it will not be included in a future release any more ?
What about the syntax ? It’s different from REST API and also the standard websocket API. Is there any document about it ? Perhaps someone who already uses it and can tell a bit about it ?

Nobody using “subscribe_entities” ?

I use “subscribe_entities” now for some days and it seems to work fine. Can I rely on this function ? I hope it will not vanish in a future release, cause its a perfect function for small MCUs.