Unless they were actually born outside, like farm cats, cats typically don't mind too terribly being housecats... and it does definitely keep them safe.
The cats here are usually chasing flying insects, but we have had a couple of mice and rats enter the house and that ended very badly for them! They may be indoor cats, but the killer instincts are still there.
Happy to spread the word about BeBlurt... it's really the sort of app this ecosystem was very much in need of!