I picked up an Eheim Jager 50w for my QT and it can't hold the temperature like my Finnix or another brand (it doesn't come on at the right temp and goes up too high before shutting off). But I suspect I got a bad one. I'm testing it out on my water change batches to see if it's just an initial glitch. I've had Jager in the past and sure, they were fine but honestly, this is just like good cars -- they all are going to have a percentage bad. You can get a controller but those go bad too. You can add monitoring that pings you when temp goes off. My plan is to go for the last and add two smaller heaters so if one goes wild, I have a little more time to react.