Not sure where you live but in places like Australia, UK etc. there are speed restrictions for certain areas.
In particular when you drop from 60km/h to 40km/h during a school zone. These are often continuously monitored by speed cameras and subject to excessive fines and often loss of license. And if you've ever been in a high end car this drop in speed is often hard to notice.
So yes, a lot of the population are constantly checking their speeds. Otherwise you at risk of losing your license and if you cause an accident going to jail.
We have speed controlled zones in the US as well and I don't see how that makes a difference. It's a speed limit, not a speed requirement. Unless you're riding the speed limit and leaving yourself no margin for error then you should be actively monitoring your speedometer with sub-minute frequency and having to glance to your side instead of down isn't going to impact you much if at all.
My point is that where I'm from I typically don't get to decide my speed because it's dictated by externalities like traffic or road conditions. I also have a pretty good idea of the speed I'm travel and when moving through speed control zones I know if I need to slow down without watching my speedometer like a hawk.
In particular when you drop from 60km/h to 40km/h during a school zone. These are often continuously monitored by speed cameras and subject to excessive fines and often loss of license. And if you've ever been in a high end car this drop in speed is often hard to notice.
So yes, a lot of the population are constantly checking their speeds. Otherwise you at risk of losing your license and if you cause an accident going to jail.