Not working plugin

Extra items work inconsistently.
When I configure a large number of extra items, the Total Item Amount parameter starts limiting them.
Since I work with a large number of items, the limit of 6 categories is not sufficient. Because of this, I cannot properly configure loot drops. For example, if an item is configured with 3 extra items, very often only 1 of them actually drops.

Important settings are missing in Configuration > Smelting.
There is no proper way to configure:

smelting tick amounts;

smelting speed specifically for wood.

Because of this, it is impossible to properly balance and configure the smelting process.

Smelting multiplier bug.
If the smelting multiplier is set higher than x3, all resources are smelted instantly, regardless of the amount of ore. This is clearly incorrect behavior and breaks game balance.

Plugin restart required after changes in Configuration > Smelting.
The changes are not applied immediately, which is inconvenient and not obvious.

I am aware of problems with the smelting configuration and they will be fixed with the next update. If you need advanced control over the smelting process (tick speed, etc.) I highly suggest you to use a plugin that is specifically designed for that. 

I think you misunderstood the use of categories. Categories are used to create a pool of items where a configurable amount is selected. 6 Categories should be more than enough for that. If you want 1 or more items to always spawn along each other, configure them as extra items. Extra items are not counted in the total item amount setting.