I put them in same purchase category as wireless shutter releases (not to be confused with wireless flash controllers 😉 ): they work, the designs change regularly (different switches, plugs, buttons, batteries, lights), the quality controls are good but not great, the companies providing them have fluid reputations and even existences. Intervalometers are more expensive than wireless shutter releases, but not expensive relative to the cost of making photographs today. All of which is to say: buy two if you need them, buy replacement batteries, and don't spend more than half an hour trying to fix one.
The Amazon consumer rankings may help you make your guess a good one.
Message was edited by: Kirby Krieger