I did skip over a few different timers when looking for some because people said they did not work well with on and off. I can tell you these particular ones are great. I have three of them now and I use them for my tanks primarily, and my home lights too.
I recommended it to a family member while going on vacation once. They picked it up and set it to the security mode. The timer would automatically turn their lights on and off randomly in the day and night, making it look like someone was home.
I have not had any issues with these ones at all. I have the two pico tanks both set to one of these timers too. Plus, at $15 if it is defective, it isn't a huge loss.