I use the relatively cheap mechanical timers. A few years ago, I tried going to the digital ones. I found the ones I was using not very dependable. The ones I tried on the water pump kept resetting. I do have a digital one on a light in a tent I use for little plants and it works great. It's been keeping time for years. I just leave it plugged in, and unplug the light from it when not in use.
I have had a couple of them crap out over the last ten years but I find them bulletproof. I keep spares of pumps and timers, so if they break, I just go grab another.