The FX888 is an older style iron where the tip and heating element are separate components, the newer generation (such as this iFixit one) have the tip, heater

The FX888 is an older style iron where the tip and heating element are separate components, the newer generation (such as this iFixit one) have the tip, heater and temperature sensor integrated as a single component which allows them to regulate the tip temperature much faster and more accurately. Hakko does make irons of that type now but they're very expensive, up in the $500 range. Another benefit of the newer style irons is the tip can usually be hot-swapped (literally while it's still hot) without having to unscrew anything, you just need something insulating to pull the tip out with.