Aqueon Pro 250W here.
Had it for over 10 months and no problems.
Like mfdrookie516 said. Mine is stable but it doesn't match the dial reading to actual temp. It is set to around 74 but keeps it right on 78-79 degrees. It is oversized for my tank so that may be why.
Kind of related. My Sybon digital thermometer was reading 52 degrees a few months ago. Needless to say I almost had a heart attack when I read that. My fish were fine so I was like WTF!? How are they still alive
Turns out the thermo was crap. So I went with an old school glass one.