You can say the same for porn in general in terms of mental health, and as for legality, it varies from state to state if you're in the US. But for where I live I did my research. It's legal as long as it doesn't involve real people (and it shouldn't EVER involve real people).

Just as an aside, I also know that Law Enforcement do not even remotely care about 2d drawn or 3dcg porn of this nature because whenever it gets reported, all it does is hinder their ability to stop the real thing.