Neurofeedback has been studied for decades, most extensively for attention regulation, and has a reasonable evidence base compared to many behavioral interventions. That said, "effective" depends heavily on what's being trained, how consistently sessions happen, and whether progress is actually being measured.
What Makes It Work, and What Doesn't
Neurofeedback works by showing the brain its own real-time activity and rewarding healthier patterns, essentially a repetition-based skill-training process rather than a passive treatment. Like any skill, it tends to work better with consistent sessions over time than with a handful of one-off visits.
The honest caveat: results vary by person, and no legitimate protocol should promise a guaranteed outcome upfront. What separates effective use from a waste of money is measurement, mapping the brain's activity before training, tracking changes at intervals, and adjusting the protocol based on what the data actually shows, rather than running the same generic program regardless of response.