I'm considering starting to bulk load as well for a few projects I have in mind.
I am worried about metal cassettes popping open on me. I have had this happen on a factory cassette when I dropped it, and the reusable metal cassettes I have (my step dad's from the '70s; old but never used) don't seem to hold closed nearly as securely as a factory cassette. I was looking at the B/H plastic cassettes instead because they have a screw top. Whatever you do end up using, let us know how it works out, as I am curious myself.