Some do, some do not. Some just put out heat. Thats why they will say something like: in a 2.5 gal raise temp 5 degrees, in 4 gal raise temp 4 degrees from the mean temp.
Others will maintain the temp you set for it. Like yours, you have to adjust them till you find the right temp, then it will maintain it. Your heater is rated for 10 gallons instead of 5, so perhaps that 50 watts puts out enough heat to maintain the 10 gal at the 78 degree temp, if you dial it to 78. But, in the smaller 5, you must dial down.
And others are very accurate and self adjusting, when set to a specific temp (lab).
Also, heaters are usually slow to heat. They can turn off and on quickly, but generate the same amount of heat over time. I have no idea what they all use for the 'turn-off' 'turn-on' guide.
I know a lot of things use metal strips to account for on/off. I suppose these heaters would use that. They are cheap. Then new computer controlled dig heaters probably use what you set for the limits.