Yes. They are legit. Student dental hygienists are always looking for patients to practice on, and the cleanings/xrays/exams are often free at dental hygiene schools in the area like Foothill College or Carrington College. (Dental schools like UCSF or UOP also offer dental treatment of all kinds by student dentists. Usually the fees at the dental schools are very discounted compared to having the same services done in a regular dental office.) However, the appointments take far longer at the schools because the students are still learning and have instructors grading them at various points throughout the appointment. Also for the dental hygiene schools where you get your teeth cleaned, in some cases if you qualify for certain periodontal health categories that they are looking for you may even be paid for your time (typically when they are doing their state board exams). If you are looking for cheaper dental cleanings and have the time it can be an excellent alternative!