I like the Isekai where MC uses his own worlds suff to exploit Arbitrage (the practice of taking advantage of price differences for the same asset in different markets). BUT i hate how 99% of them have NO regard for the consiquences of their actions. They'll introduce GUNS, and GUN POWEDER. They introduce GAS, DIESEL, OILS, AND EVEN PLASTICS! How hard is it to just take the stuff out of the wrapping and put it in wooden, or glass, containers for the more primitive world?   The worst one i saw introduced ANIMALS! Have you learned NOTHING in the history of human world population? Do you have any idea how many problems we've had from introducing animals from one place into another? EXPLOIT THE MARKETS ALL DAY AND BECOME RICH, but at least TRY not to ruin the other world!