Why don't we all watch what we are saying and remember the announcement at the top of the page. That's not up there to fill space.
Betta's that I've kept have all had very different personalities. Some have been as mellow as anything, while others will chase anything that moves (or it thinks will move, or might move at somepoint in its life). Neat little fish none the less.
Really the only way to tell is by trial and error. See what works for you, and what doesn't. To my memory, I've not had a betta kill a snail, but have watched them pick at them before.
We all like to think we follow 'rules' when it comes to fish keeping, when really they are more like 'guidelines'. Often times we have to tweak them for what works for us.