Ultrasound is the flavor of the month. The cost of the machine is soon amortized and it becomes a cash cow. Bear in line that ultrasound irritates tissue. That doesn't always sound like a good idea. It does stimulate blood and circulation in muscles, which sometimes may be a good idea. I am not a happy camper with the use of ultrasound to relieve pain from nerve entrapment.
One thing I have learned in the 6 years I've been dealing with TN is "buyer beware". There are a lot of schemes to take advantage of people in pain. I have not found any credible research regarding ultrasound and TN.
Find a good doctor with lots of facial pain experience, read 'Striking Back' a good resource book, and research before you pay a lot of money.