Your mileage will vary, but since I changed from a lower jaw soft
nightguard to an upper NTI last week here's my impression. The
nightguard is bulky and fell out the first few nights I have worn it.
The NTI on the other hand is tiny and stays in place. However, it puts
some pressure on upper and lower incissors, I also wake up with a sore
tongue since it seems to rub against the occluding element. So far I
would rate the soft nightguard higher in comfort, but if you can't
sleep with your mouth feeling full then the NTI might be a better
choice. Price for night guard ~ $200 (back in 2002), price for NTI ~
$450 (last Wednesday).

That might also reduce the willingness to wear them. My jaw clicks
when opened wide and the muscles are sore, so there was good
motivation to do something about it. The nightguard reduced symptoms
by 50%, with the NTI I have not seen any change yet (but it's only
been 4 nights so far).

My student dentist had indicated that she thought I grinded my teeth
and so should get a night guard. I said that I doubted I would be able
to wear one because I am a very light sleeper and had trouble wearing
the teeth whitening thing that was made for me a few years ago.

So then I read you guys talking about NTI and I decided to ask her
about that.

So I did and she had never heard of it. She asked another student
dentist and he had never heard of it.

Then she asked the prof, probably 60 years old.

He looked puzzled and said it was for headaches. I said, "Yes, but
apparently some dentists are using them successfully for grinding
problems."

He said, "Maybe for short term use it might be okay, especially if
grinding is giving you headaches, but long term use will probably
cause the front teeth to protrude, and also it can cause problems in
the jaw, leading to TMJ or other problems." I can't remember exactly
what he said, but it was something like that.

In any case, he was very much against it.

Seemed to me that he really didn't know much about it, though and was
probably behind-the-times in his views on this.

But what about these assertions?

Personally, the cost of a night guard OR an NTI seems overpriced to
me, and I am leaning towards not getting either one. I really have no
proof or indication, that I grind all that much in the first place. I
have never had headaches much at all (until my recent sinus lift - see
my thread on that!). So I am skeptical about my need for any kind of
guard.