Temp fluctuations?

[Oblio]

By "older heater" do you mean an older design or the actual age of the product? Cause I got this one very recently, it's only been running for a few days. (PS, it's currently running in an empty tank bc I'm waiting for the plants to arrive.) The room temp is 60 at night and 65 at day.

Both. An old design is likely to have bi-metal contacts, and as those get older they tend to stick. Newer unit will probably have electronic temp sensors and electronic switches that are much more accurate and reliable. The only unknown is cost, it may be cheaper to use the old electromechanical bi-metallic thermostats on new low-cost designs. This is where me not being a heater expert comes into play.