SECONDS BETWEEN REFILLS: 10
(Push RESET)

SECONDS BETWEEN REFILLS: 0

Which of the following has less impact on server performance?

It seems to me that 0 seconds is more lightweight than a 10-second timer running...
However, many games are less demanding in vanilla settings.

If deleted from the data file, it will be revived after an o.reload.

There won't really be a performance difference when changing this setting. The plugin follows the same logic as vanilla, which is to run a repeating timer per vending machine about every 1 second, which basically checks whether it's time to do a refill for each item (when a purchase is made, a timestamp is set stating when the next refill for that item should take place). Even if you set "seconds between refills" to 0, the timer still runs on the same 1-second schedule. It would be possible to change the plugin to disable the refill timer if all of the sold items have a restock delay of 0, but I doubt that would have a significant performance impact.

Thank you for the clear explanation.

It is not a serious impact, but I was just cautioning against minute effects that can build up and become significant.