I give it 6/10.
It's not bad, as alchemist fantasies go, but it's a bit generic, and ít gets demerit points for succumbing to the old "I guess I gotta have a (hot girl) SLAVE to keep my secrets but it's OK because slaveholding in this country is highly regulated and GOOD actually" trope.
(Seriously, magical NDAs should be if anything easier and cheaper to make than slave contracts. )
It seems one character was captured and illegally sold as a slave, and even after that was revealed, they remain a slave. So, allow me to doubt the benevolence of the slave trade in this setting.
The story suffers a bit from shallow thinking on part of the author. Like, a quick research session tells me that mining copper, silver and iron in the same mine is possible, but having them in equal amounts is highly unusual and probably you'd have copper/silver mixed in a ratio that's 1% copper, 0.001% silver, and the rest rock. iron ore might be in separate larger deposits, or it could be the same ore that's also 10% iron.
If the author did this research and presented it in the manga, it would be interesting trivia, but they didn't. They could say that mana naturally causes metals to separate and gather, but didn't bother. So it comes across as game-logic.
And the author introduces purification magic to remove fecal waste, but what about preservation of mass? If his magic toilet becomes a household item, it might leech nitrogen and carbon from the local ecosystem.
Going more than one layer deep on these things would enrich the worldbuilding, and I don't feel it's unreasonable for me to expect an alchemy manga to have a grounding in chemistry.