Re- reading your question, I realised I hadn�t actually answered your real questions.
You need to go to a dentist to check you can benefit. From your comment about it helping someone who hasn�t brushed their teeth in a few years, I gather if it�s not you they�ve not seen a dentist for a while either which may bring up a few other issues.
Long term risks � again, normally not if under dental supervision, but any underlying risk to the tooth enamel needs assessing first.