In the hakko line, fx-951 is the step-up which uses a heater and sensor in the tip (t15/t12 tips).
The alternative, for a hobbyist, would be something like this new iFixit iron, the Pinecil, Miniware TS80/TS100 or one of the variety of chinese irons from amazon and Aliexpress that take Hakko T12 tips (Quicko and similar).
On the high-end, professional side, it's JBC and Metcal. Expensive.