You'd be better off with an ordinary digital thermometer, which would be cheaper and at least as accurate. And if you dropped it in your developer tray it would be less of a disaster! Don't confuse accuracy with consistency by the way, most digital thermometers are only accurate to +/- 1 degree C but if calibrated to a master mercury or similar device will maintain that calibration very well, usually to within +/- 0.2 C or better.