Doesn't directly cost users extra gas, re-executions are absorbed by the chain. The cost is to overall chain throughput, which can surface as higher base fees during congestion. More on /docs.
Caveat Stats are aggregated over the time window selected at the top of the page. The default is the last 7 days; switch to "All time" to cover every block pev has indexed, or narrow to 1h / 24h to see only recent behavior. The "avg parallelism" is the average score of every block this contract appeared in within that window (not a per-tx measurement). The contract name is shown when verified on Sourcify (rare on Monad mainnet right now); otherwise we show the short hex. To get yours labeled, verify it at sourcify.dev.