I'm a researcher in formal verification; my thesis was building a tool to do this kind of stuff and I agree with the grandparent (though I would say probably closer to 5-10x slowdown not 100x).

Proofs are hard and often not for interesting reasons; its stuff like proving that you won't overflow a 2^64 counter which you only increment (aka something which won't happen for another couple billion years).

Current tools are only useful for specific kinds of problems in specific domains; things where a life really depends on correctness. Outside of those cases, lightweight techniques provide much more bang for your buck imo.