I bought my wife a Thermapen for Christmas and it’s revolutionized her cooking (and mine). She’s using it for everything except toast and boiling water. Chicken, steaks, roasts, fish, fudge, cakes, casseroles, anything where complete cooking can be determined by internal temperature. The margin between perfect and overcooked fish can be slim, and she likes steak as rare as possible. This thing lets her nail it every time with no fiddling around.
Yes, we have cheaper thermometers. The difference is night and day. More than anything, it’s the speed with which it settles, but the unit is also calibrated, which gives us confidence. (I spent some time looking for a cheap alternative, but didn't find anything with consistently great reviews. I decided it was worth the extra money to buy less hassle, and I went with Thermoworks. No regrets!)