Choosing sleep meds

I'm a therapist and I saw a client recently on low-dose mirtazapine for sleep. Apparently it's very powerful because the client found it even more effective than low-dose quetiapine.

I rarely see this. Often it's trazodone, doxepin, quetiapine, hypnotics, and occasionally benzos. Not mirtazapine. Don't know much about mirtazapine, but I assume at that dose it acts like an antihistamine, which is probably also true of doxepin or quetiapine. Is there any particular reason mirtazapine is not prescribed more? Specifically, compared to quetiapine. I know it's associated with increased appetite and weight gain, but many people gain weight on quetiapine too. From what I can tell, olanzapine and clozapine are probably worse, but don't see clients on those meds for sleep. And with quetiapine, there is also a risk of movement disorders, though probably not very likely at that dose. Anyways, given that nearly all psychiatric meds (SSRIs, tricyclics, anticonvulsants, antipsychotics) come with significant immediate and long-term side effects, I'm curious how you guys decide which meds to try first (e.g., mirtazapine before/after quetiapine).