Betaine and TMG are one and the same.
It is common practice to use the betaine name
when writing the chloride salts name which is
betaine hydrochloride. The salt form is commonly
used to increase gastric acidity. Some people
take 40, 50, 60, 70, even 80 grains of betaine HCL
to replace the portion of HCL no longer produced
by the aging stomach mucosa. If there is too little
acidity in the stomachs contents ( the chyme)...that
mucus coated food, the pepsin is inactive thus slowing
digestion and the gastric motility is excessive . The result can be
bile reflux into the stomach and even into the esophagus
which  irritates the stomach lining and esophagus.
Interestingly some GERD sufferers take betaine HCL to
prevent acid reflux though they also have often made other
changes such raising the head of their beds, sleep in
adjustable hospital style beds, or sleeping in the "Lazy Boys"
recliners. I wouldn't try betaine HCl if you have an inflamed
esophagus until it is healed and you've changed your sleeping
position incline.  Some suggest as much incline as
30 to 40 degrees from level.

           +
3(CH3)NCH2COO-

            +
3(CH3)NCH2COO-   HCL