If there's an RCBS cowboy set for it, I'd go that way. My understanding is those use a stepped expander like a Lyman "M" die for "belling" the case mouth. It's not a necessity, but a nice thing to have.
Flex tips require you to trim your brass to a length that only works for them, so they'll cycle in lever actions. The Hornady manual states the specific trim length for them. That's their big drawback for reloaders.