Your research is correct. Under 100mg, it acts like a completely different drug than it does at 150mg (XR) and higher.

It's given at 25-75mg for help sleeping, and <25mg for help with anxiety, agitation, anger, etc.

It will still act as a mood stabilizer because of its sedative effects. It will dull out
any sort of emotion. When you hit the levels that it was actually approved for, though,
you hit a total and complete "zombie" level.

Also, Seroquel IR (instant release, normal form) isn't really given all that often as a mood
stabilizer or to counteract psychotic symptoms. Seroquel XR (extended release) is used much more often
these days for treating those.