I think it's better at 4 years old to buy a watch with hands to start learning the time. But if he already knows the time, yes, that could be a good option, but he's likely to keep touching the buttons and it will go out of adjustment. That's my opinion. 🤷🏼♀️
Our child had it at age 3.5 and was happy with it. It is a bit large for a 4-year old, but very robust. The main issue was, that our child kept playing with the buttons and knobs and thereby changed the time or set alarms. So it depends on the child :-)