i have one. a large female named Lulu. in my experience, she's a pretty placid betta. i mean, she flares with the best of them, and is really jumpy(she often splashes about in her tank at night. while i'm trying to sleep. bugger.). but, she submits to my much smaller veiltail female, Caroline(they're in their separate tanks, but able to see each other. they flare, Lulu gets the submission bars and stops flaring). but, i've never had her in with any other fish. ever. .__. so, with other fish, i'm not sure.
then again, Lulu's odd. scared of tanks larger than a gallon. >.>;