When this mod is enabled, Hydro Plants from Maraxis lose the Salt Electrolysis recipe, only allowing EM plants and the Krastorio Electrolysis plant to craft it.

Correct, yes. This is already communicated on the information tab.

Is there a reason why it can't be on both? A mod setting toggle would be appreciated.

The silver lining early on for the Hydro plant having 50% innate quality is that at least quality salt gives you more molten salt, and later on it's nice to match the quality of wyrm specimens (which can only be made within the hydro plant, forcing the 50% quality) for the planet's science. The EM plant recipe is already there for people who don't want to interact with quality, so I don't understand what this change is intended for.

Sure, I can allow both. I'll put it on the to-do list. Honestly I approached Maraxsis like most planets, where I just do no quality, then legendary everything when I unlock it.

Thank you. I normally do it that way too, but I installed additional quality tiers this run and it's a bit more cumbersome to wait until I have the capability to make max quality before I start engaging with it.

0.18 adds a new setting for this. With the setting enabled (default) it sets the crafting category to K2's electrolysis. With it disabled, it instead just adds the crafting category so you can do in either machine.